Method and apparatus for rearing post-larvae shrimp

A method and apparatus for rearing post-larvae shrimp wherein the shrimp are retained for an initial post-larvae period of growth in a first shrimp rearing means including a first habitat means comprising a first plurality of stacked substrates having a first combined total surface area and wherein the shrimp are retained for at least one subsequent period of growth in at least one further shrimp rearing means including a second habitat means comprising a second plurality of stacked substrates having a second combined total surface area greater than the aforesaid first combined total surface area. In further aspects of the invention, unique filtration means and culling means are also disclosed.

BACKGROUND OF THE INVENTION 
This invention pertains to a method and apparatus for rearing shrimp and, 
in particular, to a method and apparatus for rearing post-larvae shrimp 
under controlled conditions. 
In recent years attempts have been made to rear post-larvae shrimp under 
controlled conditions. Rearing shrimp in this manner has been carried out 
employing so-called intensive culture systems and methods. 
Systems of this type have been proposed wherein the post-larvae shrimp are 
reared in a succession of units each being provided with habitat 
structures for the shrimp. U.S. Pat. No. 3,658,034 issued on Apr. 25, 1972 
discloses one such system wherein the initial unit of the system comprises 
a tank provided with a habitat structure formed from a plurality of 
vertical substrates. Following this initial unit, are a number of further 
units which include tanks of increasing size and each of which is provided 
with a habitat structure formed from a number of cylindrical enclosures 
each for housing an individual shrimp. In this system, the tanks are 
disposed below one another so the shrimp content of a higher tank can be 
emptied into a lower tank when the shrimp in the higher tank have 
undergone a desired degree of growth. Moreover, in this system, the water 
in each tank is continuously circulated to remove contaminants therefrom. 
Further U.S. patents which disclose intensive culture systems wherein 
vertically or horizontally aligned substrates provide habitats for 
post-larvae shrimp are as follows: U.S. Pat. No. 3,985,101 issued on July 
2, 2975; No. 3,916,833 issued on Nov. 4, 1975; and No. 3,899,639 issued on 
June 17, 1975. In the last named patent, the intensive culture system 
disclosed comprises a plurality of horizontally arranged nets and a 
filtration system whose filter is backwashed by drainage of some of the 
water of the system. Moreover, in this system, light is directed through 
the central area of the nets to attract molting shrimp to such areas and 
thereby prevent these shrimp from being cannibalized by the remaining 
non-molting shrimp. 
It is an object of the present invention to provide an improved system and 
method for rearing shrimp under controlled conditions on a commercial 
scale. 
It is a further object of the present invention to provide a system and 
method for rearing shrimp wherein use of the rearing volume is maximized 
in a manner that does not contribute to shrimp mortality. 
It is yet a further object of the present invention to provide a system and 
method for rearing shrimp wherein filtration of the rearing medium is 
carried out in an advantageous manner. 
SUMMARY OF THE INVENTION 
In accordance with the principles of the present invention, the above and 
other objectives are realized in a system and apparatus comprising a first 
shrimp rearing unit for retaining shrimp for an initial post-larvae shrimp 
growing period including a first habitat structure formed from a first 
plurality of stacked substrates having a first combined total surface area 
and at least one further shrimp rearing unit for retaining shrimp for a 
subsequent shrimp growing period including a second habitat structure 
formed from a second plurality of stacked substrates having a second 
combined total surface area greater than the aforesaid first combined 
total area. 
More particularly, the first combined total surface area is selected so 
that the unit area per shrimp of the first plurality of substrates is 
sufficiently large to encourage and promote the growth of shrimp of sizes 
encompassed by the first shrimp growing period. The second combined total 
surface area, in turn, is selected to be greater than the first by an 
amount which results in a unit area per shrimp of the second plurality of 
substrates which is sufficiently large to encourage and promote the growth 
of shrimp of sizes encompassed by the second shrimp growing period. 
Preferably, the total second surface area and the unit area per shrimp of 
the second plurality of substrates should be from 25 to 200 percent 
greater than the total first surface area and the unit area per shrimp, 
respectively, of the first plurality of substrates. 
By providing both the first and second rearing units with habitat 
structures formed from stacked substrates, the volume of the units for 
rearing shrimp is maximized for both the initial and subsequent 
post-larvae growing periods. Moreover, the use of stacked substrates for 
the subsequent growth period is found to better promote shrimp growth and 
life as compared to systems using other types of habitat structures for 
this growth period. 
In a further aspect of the invention, the system is additionally provided 
with a filtration system which accomplishes filtration of the rearing 
units through the use of a single pump. The remainder of the filtration 
system operates via gravity flow. The aforesaid filtration system is 
additionally provided with uniquely constructed filtration assemblies 
(i.e., particulate filters, bio-filter, carbon filters and foam 
fractionator) for appropriately filtering the medium of the rearing units. 
The system and method of the invention also contemplate the use of a novel 
technique and apparatus for movement of the shrimp from one unit to the 
other and for eventually harvesting same.

DETAILED DESCRIPTION 
FIG. 1 illustrates an overall view of an intensive culture system or unit 1 
for rearing post-larvae shrimp in accordance with the principles of the 
present invention. The system includes a shrimp rearing area 2 comprised 
of three adjacent shrimp rearing units 2A, 2B, and 2C and a filtration 
area 3 adjacent the rearing unit 2C. The rearing units 2A, 2B and 2C 
comprise rearing tanks 4A, 4B and 4C whose walls are formed from cinder 
blocks as are those of the filtration area 3. A further cinder block area 
forms a walkway 5 around the rearing units and the filtration area. This 
walkway and the walls of the rearing tanks and filtration area support a 
frame structure 6 on whose exterior is placed a plastic roof 6A (See, 
FIGS. 2 and 3) so as to form a fully enclosed system. Advantageously, in 
the area of the rearing units the plastic of the aforesaid roof is clear 
so that the roof acts to couple solar energy into the system for heating 
same. 
The rearing tank 4A of the rearing unit 2A holds post-larvae shrimp of an 
initial stage or period of post-larvae growth, while the tank 4B of the 
unit 2B holds shrimp who have completed this initial period of growth for 
a second growth stage. The tank 4C of the unit 2C, in turn, holds shrimp 
who have undergone the aforesaid second growth stage and until the shrimp 
reach maturity. As is apparent, the rearing tanks increase in volume, in 
going from the tank 4A holding the shrimp who are in the initial 
post-larvae growth stage to the tank 4C holding the shrimp that reach 
maturity. In the present illustrative case, this is accomplished by 
increasing the length of the tanks, while maintaining their widths 
constant. The purpose of this increased volume is to permit the use in the 
rearing units of habitat structures comprised of stacked substrates which 
increase in total surface area in going from the rearing tank 4A to the 
rearing tank 4C. This increased surface area accommodates the increase in 
size of the shrimp, thereby affording sufficient habitat area for 
promoting growth while maximizing the volume of the tanks useable for 
rearing. 
As shown in FIG. 1 and 2, the rearing units 2A, 2B and 2C thus include 
habitat structures 7A, 7B and 7C. The aforesaid habitat structures 7A, 7B 
and 7C are advantageously all constructed from a basic substrate unit 9, 
the larger area structures being provided with an increased number of 
units to provide the increased area. 
In the present illustrative case, the habitat structure 7A includes eight 
substrate units, the habitat structure 7B, sixteen susbtrate units and the 
habitat structure 7C, forty substrate units. The substrate units of each 
habitat structure, in turn, are arranged in banks 11 formed of one or more 
columns of substrate units (FIGS. 1, 2 and 3). Each such bank is supported 
on a common rectangular frame 12 which permits the bank to be inserted and 
lifted from the tank of its respective rearing unit. As shown, the 
substrate units of the banks are tied to their resepctive frames so they 
hang therefrom upon insertion into the rearing tanks. 
The substrate banks 11 are lowered and raised from their respective rearing 
tanks via the lines 13 of individual pulley systems 14 associated with the 
banks and supported on the frame 6. These pulley systems, in turn, are 
activated by winches (not shown) also supported on the frame. When lowered 
into the rearing tanks the banks 11 are maintained at a predetermined 
height above the tank bottoms. This facilitates feeding of the shrimp as 
well as filtration of the tanks and clearing of the tank bottom. The banks 
are also maintained below the surface of the medium 15 in their respective 
tanks. 
As shown in FIGS. 3 to 5, each of the substrate units 9 comprises a three 
dimensional open rectangular frame 21 formed of tubing members. Stretched 
across opposite sides of the frame are a plurality of parallel substrates 
22 which, as shown, are formed of meshed screening. These horizontally 
displaced vertically arranged stacked substrates or screens 22 serve as 
the habitats for the shrimp who crawl up them. The spacing between the 
substrates 22 of each substrate unit 9 is dependent upon a number of 
factors, such as, for example, the rearing unit in which the substrate 
unit is to be situated, the size of the shrimp in such rearing unit, etc. 
Typically, the spacing may be in the range of b 2 to 3 inches depending on 
the aforesaid factors. 
As above mentioned, the increase in total surface area of the substrates of 
each habitat structure relative to that of the preceding structure is 
dependent upon the increased unit area per shrimp required to sustain and 
encourage growth of the shrimp in each particular rearing unit relative to 
that required in the preceding unit. The unit area per shrimp for 
encouraging growth in a particular rearing unit, of course, will depend 
heavily on the growth stage associated with that unit, as relatively 
larger growth stages will result in shrimp of relatively larger increased 
size and will require a proportionally relatively larger unit area per 
shrimp to encourage growth. The number of growth stages employed, in turn, 
is dependent upon the desire to limit the system and, hence, the growth 
stages to a minimum so as to preserve compactness and minimize labor, 
while at the same time affording a sufficient number of growth stages so 
that the difference in size of the shrimp in each stage and, hence in a 
given rearing unit tank, is not such as to permit a large degree of 
cannibalism of the smaller shrimp by the large shrimp. 
With these conditions in mind, it has been found that the growth stages 
subsequent to the initial stage may encompass an increased growth in a 
range from 25 to 200 percent before either the number of rearing units 
becomes too large, or the difference in the size of the shrimp in each 
stage results in excessive mortality due to cannibalism. This means that 
each growth stage subsequent to the initial stage may encompass an 
increase in size of from 25 to 200 percent which, in turn,means that the 
increase in total substrate area and, hence, unit area per shrimp from one 
rearing unit to a subsequent unit will also be approximately in the range 
from 25 to 200 percent. 
In one embodiment of the present invention, it has been found desirable to 
select the initial growth stage to encompass a 200 percent growth from 
post-larvae size and each of the subsequent growth stages a 100 percent 
increase in growth relative to the preceding stage. Thus, with this 
embodiment of the invention three growth stages are required for the 
shrimp to increase in size from their initial post-larvae size of 
approximately one-half inch to their adulthood size of 6 inches. In 
particular, the initial stage covers the growth period from 1/2 to 3/2 
inches, the second stage from 3/2 to 3 inches and the final stage from 3 
inches to 6 inches. Furthermore, in this embodiment, the number of rearing 
units is three, as depicted, and the substrate units of the rearing unit 
holding the shrimp in the final stage have a total combined surface area 
which is 100 percent greater than that of the units holding the shrimp in 
the middle stage, the surface area of the latter sustrate units, in turn, 
being 100 percent greater than that of the units holding the shrimp in 
the initial stage. Additionally, in this embodiment, the number of 
substrate units per stage is as depicted in FIG. 1, and the first and 
second growth stages each cover approximately a 6 week period and the 
final growth stage covers approximately a 3 month period. 
In order to further facilitate rearing of the shrimp and to further prevent 
the cannibalistic tendencies of the shrimp from increasing mortality, each 
rearing unit 2A, 2B and 2C is further provided with molting areas which 
act as sanctuaries for molting shrimp who have lost their outer shell and, 
therefore, are prone to attack from non-moltng shrimp. As shown, these 
areas are provided by mesh netting sections 23 which are attached to the 
frames 12 and hang therefrom above the substrate banks 11. When the banks 
11 are lowered into their respective rearing tanks these netting sections 
lie within the tank medium immediately above the substrate units, and 
hence, are accessible to molting shrimp whose tendency when molting is to 
seek shelter away from the other shrimp. 
To further facilitate use of these molting platforms, the netting sections 
23 are provided with means for creating high and low spots relative to the 
substrate units. This is simply and easily realized by attaching leads 24 
and floats 25 at alternate positions along the netting. The low spots 
provide areas where the molting shrimp can attach themselves to the nets 
and the high spot areas where the attacked shrimp can crawl to isolate 
them further from the other shrimp. Additional isolation is achieved by 
providing dim lighting in the area of the netting sections 23, this being 
accomplished by lights 26 attached to the frame 6 and directed at the 
sections. 
In order to facilitate the transferring of the shrimp from the rearing unit 
2A to the unit 2B and from the rearing unit 2B to the unit 2C and to 
facilitate the removal of adult shrimp from rearing unit 2C, a similar 
culling apparatus is provided in each of the rearing tanks 4A, 4B and 4C. 
This apparatus permits selection of the shrimp who have reached the 
desired stage of growth of development to be transferred to or removed 
from their respective rearing tank quickly and efficiently. More 
specifically, as illustrated in FIGS. 12 through 15, each tank is provided 
with a slotted track 121 which extends substantially around the periphery 
of its four walls and whose ends terminate adjacent an elongated opening 
122 closed by a screen 123 in the wall of the tank adjacent the next tank. 
The track 121 provides a guide means for a net structure 124 whose ends 
are moved in opposite directions so as to provide an enclosed area 147 
including the screened opening 122. 
More specifically, the net structure 124 comprises two similar elongated 
hollow bars 125 and 126 each of which is provided with a guide structure 
127 at its upper end. The guide structure comprises two horizontal rails 
128 and 129 which are crossed by two vertical rails 131 and 132. The upper 
horizontal rail 129 carries at its opposite ends horizontally oriented 
rollers 133 and 134. The lower horizontal rail 128 also carries at its 
opposite ends rollers 135 and 136, these rollers being oriented 
vertically. Inboard of the rollers 135 and 136, the rail 128 supports two 
wheels 137 and 138 arranged with their axes vertical. Two further wheels 
139 and 141 having horizontal axes are connected via bars 142 and 143 to 
the lower ends of the vertical rails 131 and 132. 
Inserted in each of the hollow bars 125 and 126 is a tubular plactic member 
144. The members 144 support opposite ends of a mesh net 145. The net 145, 
in turn, passes through vertical slots 146 in the bars 125 and 126 and its 
draw strings are gathered together at a common point above the top end of 
one of the bars. The net 145 is further provided with leads 148 and floats 
149 which maintain the net in a vertically stretched condition. 
In operation, the net structure 124 is placed in a respective tank with the 
wheels 137 and 138 of the guide structures 127 of the bars 125 and 126 
inserted in the track slot. The rollers 135 and 136 and the wheels 139 and 
141 of the guides, in turn, engage the upper and lower walls of the track 
to prevent tilting. The two bars 125 and 126 are then moved in opposite 
directions until each arrives at an end of the screened opening 122 in the 
tank wall. During such movement, the wheels 133 and 134 of the guide 
structures ride on the inner wall of the tank to further guide the net 
structure. With the two bars 125 and 126 adjacent the ends of the opening 
122, the net 145 now forms the enclosed area 147, which area includes the 
opening 122 and surrounds substantially all the shrimp in the tank. The 
draw strings of the net 145 are then pulled, allowing those shrimp who are 
smaller than the openings in the net to escape. The aforesaid openings are 
selected to be approximately equal in size (i.e., about 10 percent 
smaller) than the size of shrimp who have undergone the stage of 
development associated with the particular rearing tank. As a result, the 
shrimp who remain trapped in the localized area 147 surrounding the 
opening 122 are those who have substantially undergone the desired degree 
of growth. The screen 123 closing the opening is then slid upward and the 
aforesaid trapped shrimp move through the opening. If the tank in which 
the net structure is placed is either one of the rearing tanks 4A or 4B 
the shrimp are transferred to the subsequent rearing tank, either the tank 
4B or 4C. If on the other hand, the tank is the last rearing tank 4C, then 
the shrimp enter a harvesting container and are removed from the system. 
As above-mentioned, the system of the invention is also provided with a 
filtration area 3 located adjacent the rearing unit 2C. This filtration 
area provides filtration for the rearing tanks of the rearing units and 
maintains the medium 15 therein substantially contaminant free. 
More particularly, as shown in FIGS. 1, 2 and 6, the filtration area 3 
comprises a tank 31 which is partitioned by walls into a bio-filter 
fractionator section 32, a foam fractioner filtration section 33, a carbon 
filter filtration section 34 and filtration inlet and outlet sections 35 
and 36. The tank 31 also supports a particulate filter filtration assembly 
37 which is situated above the bio-filter section 32 and a pump 38 which 
is situated on the tank wall separating the foam fractionator and carbon 
filter sections 33 and 34. The filtration inlet section 35 borders an 
aperture 41 closed off by a screen 42 in the wall of the rearing tank 4C. 
Medium 15 from the rearing tank 4C, as well as the medium from the rearing 
tanks 4A and 4B and flowing into the tank 4C through the screened 
apertures 43 and 44 (see, FIG. 1), thus enters the inlet section 35 
through the screen 42. A cylindrical conduit 45 connects the intake of the 
pump 38 to the inlet section 35 and the pump 38 raises the energy of the 
medium flowing into the inlet section to a level or head sufficient to 
carry the medium, via gravity flow, through all the filtration sections 
and back to the rearing tanks. Filtering is thus carried out using a 
single pump and gravity flow, thereby minimizing the energy requirements 
needed for operation. 
More specifically, the medium entering the pump 38 is coupled to the pump 
output which feeds a manifold 46 which couples the medium to cylindrical 
inputs 47 of the particulate filter assembly 37. These inputs feed a 
plurality of particulate filters 100 forming the filter assembly 37 and 
supported above the bio-filter section 32 on the walls of tank 31 forming 
same. The medium passes through the filter assembly 37, descends down 
through the bio-filter section 32 and is collected in apertured pipes 48 
at the bottom thereof. The pipes 48, in turn, lead to a collector pipe 49 
which carries the medium through an aperture 51 in the tank wall bordering 
the foam fractionator section 33. The medium then passes through the foam 
fractionators 81 and is carried by a coupling pipe 52 to the carbon filter 
section 34. After passage through the filter substrates 91, the medium 
enters the filter outlet section 36 and is coupled therefrom back to the 
rearing tanks 4A through 4C by a return pipe 53. 
As above discussed, the particulate filter assembly 37 is formed from a 
plurality of similar particulate filters 100, each of which receives 
medium to be filtered via the manifold 46 connected to the output of the 
pump 38. The filters 100 filter particulate matter from the medium passing 
therethrough and operate on a backwash principle. As shown in FIGS. 7 
through 9, each of the filters 100 is in the form of a cylindrical drum 
having opposite flat ends 101 comprised of a stiff material such as, for 
example, plexiglass. A plurality of support ribs 102 extend between the 
drum ends and support a layer of fine mesh net 103. The net 103 forms the 
cylindrical sidewalls of the drum and its ends are also attached to the 
drum ends. Extending centrally through the drum and rotatably mounted 
relative thereto is a conduit 108 whose input end forms one of the inputs 
47 connected to the manifold 46. In the interior of the drum, a feed pipe 
104 having an apertured end 105 branches off in a downward direction from 
the central conduit 108 and couples medium entering the drum input 47 to 
the lower portion of the drum. Slightly downstream from the feed pipe 104, 
the conduit 108 is blocked by a wall 106 beyond which a further feed pipe 
107 extends upwardly toward the top portion of the drum. The feed pipe 107 
couples filtered matter to the output end 119 of the conduit 108 which, in 
turn, is connected to a collector pipe (not shown) for carrying the matter 
out of the filtration area. The filtered matter is fed to the feed pipe 
107 from a tray 109 located in the upper portion of the drum and having 
slanted side walls which lead to the pipe 107. The tray 109 receives this 
matter from the upper mesh portions of the drum when the matter is 
dislodged by the action of water sprayed from a spray bar 111 situated 
above the drum and extending along its length. Water is controllably fed 
to the spray bar 111 through a solenoid valve 112 which is coupled to a 
water source (not shown). 
A float switch 113 supported on the central conduit 108 provides actuation 
of the solenoid valve 112 as well as a motor 114 provided for rotating the 
drum relative to the conduit 108 and the tray 109. The motor 114 drives a 
first sprocket wheel 115 which, in turn, drives via a chain 116, a second 
sprocket wheel 117 whose hub is connected to the drum end wall 101. 
In operation, when the particulate matter filtered by the interior of the 
lower portion of the mesh of the drum builds up to a point where the 
medium 15 in the drum rises to a level at which it activates the float 
switch 113, the switch 113 then actuates the motor 114 and solenoid valve 
112. This, in turn, causes the drum to rotate so that a clean section of 
mesh is now situated at the lower portion of the drum. Simultaneously, a 
clogged section of mesh at the upper portion of the drum is brought under 
the spray now being delivered from the spray bar 111. These actions cause 
the medium level in the drum to decrease and the particulate matter 
dislodged by the spray from the interior of the mesh to fall into the tray 
109 and be carried out of the system. This will continue until the medium 
level in the drum decreases to a point where the float switch 113 is no 
longer activated. At this time, the motor 114 and solenoid 112 turn off 
and the medium passes through the mesh net until the interior of the net 
becomes sufficiently clogged to allow the medium to build to a level where 
it again activates the switch 113. 
The particulate filters 100 thus remove a significant amount of particulate 
debris from the medium 15 being delivered by the pump 34 as the medium 
passes downward through the filters into the bio-filter section 32. As 
shown, the latter section encompasses a large enclosed area of the tank 
31. This area is filled with a layer of coral rock gravel 71 which is 
impregnated with nitrification bacteria. Passage of the medium 15 through 
the bio-filter thus results in removal of a significant amount of 
metabolic wastes. 
As noted previously, below the gravel 71 in the bio-filter area 32 are 
disposed apertured pipes 48 for receiving the medium after it has passed 
through the filter. These pipes carry the medium to the collector pipe 49 
which leads the medium through the aperture 51 in the wall 72 separating 
the foam fractionator section 33 from the bio-filter section 32. 
As above-indicated, the foam fractionator section 33 includes four foam 
fractionator 81 each of similar construction, for removing further 
contaminants and, in particular, large organic molecules such as proteins, 
from the introduced medium from the pipe 49. As shown in FIGS. 6, 7, 10 
and 11, each fractionator 81 comprises a pipe 82 having helical 
indentations 82a along its length and apertures 83 at its upper end for 
receiving the introduced medium. A cylindrical collector or funnel 84 is 
supported centrally within the pipe 82 and extends downwardly past the 
apertures 83. At the lower end of the pipe 82, an apertured annular bar 85 
is provided for introducing air to the downwardly flowing medium. The bar 
85 receives air from an air line 86 coupled to an air source (not shown). 
As can be appreciated, the medium flowing into the fractionator section 33 
rises to the height of apertures 83 in the pipes 82 of the fractionators 
81, thereby causing medium to descent downwardly through each pipe. The 
air introduced from the respective bars 85, in turn, causes bubbles to 
ascend upwardly through each pipe. These ascending bubbles interact with 
the descending medium causing large organic molecules to be stripped 
therefrom. The bubbles with the attached organic molecules then continue 
their upward ascent and are collected by the respective collectors 84. The 
collected material in the collectors is then conveyed out of the system by 
the lines 87 and discarded. 
The foam fractionators 81 thus remove further waste material from the 
medium 15 which, after reaching the bottom of the fractioner section 33, 
is coupled by the pipe 52 to the carbon filter section 34. This section 
includes a plurality of hollow substrates 91 which are filled with carbon. 
The hollow substrates 91 are slidably retained for easy removal and 
replacement between pairs of vertical channels 92 affixed to opposite 
walls of the carbon filter section 34. The medium passes from the pipe 52 
through the substrates 91 and then enters the outlet section 36. The 
return pipe 53 then carries the filtered medium back into the rearing 
tanks 4A to 4C. 
As can be appreciated, the combined effect of the particulate filters, 
bio-filter, foam fractionators and carbon filters of the present invention 
results in a significant amount of contaminants being extracted from the 
medium of the rearing tanks. As a result, the quality of the medium is 
maintained at a high level, thereby promoting shrimp growth and limiting 
shrimp mortality. 
A further cleaning operation can also be carried out to aid the filtration 
system in maintaining the medium quality. This cleaning operation results 
in cleaning the bottom walls of the rearing tanks along which debris which 
cannot be effectively filtered is gathered. More particularly, a 
conventional automatic pool cleaner, suitably modified, is inserted into 
each tank after the substrate units have been raised from the medium. This 
robot scrapes the tank bottom and any accumulated detritus material is 
removed and carried out of the rearing building by suitable piping. 
In all cases, it is understood that the above-described arrangements are 
merely illustrative of the many possible specific embodiments which 
represent applications of the present invention. Numerous and varied other 
arrangements can readily be devised in accordance with the principles of 
the present invention without departing from the spirit and scope of the 
invention.