NationalLibraryOfScotland/medical-history-of-british-india huggingface dataset:
6
are small in proportion to the length of the body. The whole aspect of the
larva is in marked contrast to that of larvæ to which projecting angles and hairs
give a spiny look. ( Melanoconion, Culex, etc.)
The head is smooth, and projecting hairs are inconspicuous. The clypeus
forms a prominent boss, on which are situated, in some species, hairs very closely
resembling the clypeal hairs of anopheles (Pl. III, figs. 9, 10, 11). The
antennæ (Pl. II, figs. 4 and 5), are very distinctive. They are very small and
feeble and appear to have undergone degeneration. They are quite smooth and
free from the numerous small thorn-like spines which cover the antenna of most
other genera. The large hairs of the basal tuft are represented, as in anopheles,
by a small branched hair or in some species by a single short bristle only. The
median and terminal spines so conspicuous in Culex, Melanoconion, etc., are
represented only by several extremely small spike-like processes. As a rule, the
terminal papilla (sense organ ?) is well developed and rather conspicuous. On
the whole, the antenna of Stegomyia larva approximates most nearly to that of
anopheles, but in several points is still more rudimentary than in this sub-family
(compare figs. 1 and 5, Pl. II).
The mental plate of S. sugens is shown in Pl. III, fig. 1. Those of S. fas-
ciata and S. scutellaris are very similar.
The siphon tube is very short and stout. The siphonic index is 2 or even
slightly less. The spines on the siphon vary in number according to the species.
They extend as a rule about two-thirds up the tube. There are mosquitoes,
in which the larva has tubes closely resembling those of Stegomyia, which do
not appear to belong to the genus ; some of these have other features approxi-
mating to those of Stegomyia and may be really related to the genus.
The anal papillæ are large and well developed.
Specific variation. —Three species were examined : S. sugens, S.fasciata,
and another species, probably S. scutellaris. The following variations occurred :—
Clypeal hairs. —These hairs in S. fasciata remarkably resembled those of
anopheles. The external hairs were long and simple. The two inner hairs were
shorter and branched. In this species five or six branches were present. In
S. sugens the inner hairs appeared to be absent and the clypeal hairs consisted
only of two outer simple hairs. In larvæ which were probably those of S.
scutellaris the clypeal hairs were very striking. In this case each outer hair was
double and the inner hairs were conspicuously branched (Pl. III, figs. 9, 10, 11).
The antenna.—The basal tuft in S. sugens was represented by a small hair
divided into three or four branches. In S. fasciata a single small hair only was
present (Pl. II, fig. 5).
The anal papillæ. —In S. sugens and S. fasciata these were of moderate
size, but in the larva of a third species ( S. scutellaris ?)they were extremely large,
7
and had obtuse ends. In this species the anal papillæ appear to act as func-
tional gills, since the larva had a habit of remaining long periods at the bottom.
The siphon tube. —In the case of some species a variation in the number of
spines was noted. In S. sugens and S. fasciata these spines numbered about
18. In S. scutellaris they were only nine in number. Some variations in the
exact number was, however, noted in the same species.
The nymph of Stegomyia. —The shape of the respiratory trumpets in this
and the allied species Desvoidea are characteristic. The trumpet is short and
widens rapidly towards the free end. In mounted specimens the trumpets appear,
from flattening, to be broadly triangular. A notch, as shown in the figure, is
present (Pl. I, figs. 3 and 4). In the wide trumpet opening, Stegomyia again
approaches most closely the anophelina. In anopheles, however, the trumpet is
rather flap-like and still more open than in Stegomyia (Pl. I, figs. 1 and 2).
Desvoidea.—I have not had an opportunity of seeing the larva and nymph
of this genus, but Theobald gives a drawing of the respiratory trumpet of the
nymph which is indistinguishable from that of Stegomyia (Pl. I, fig. 5). The
extremely degraded antenna figured by Theobald (Pl. II, fig. 6) also closely
resembles that of Stegomyia. The siphon tube is also short. Index 1.7. In addi-
tion James also notes that the larvæ adopt a vertical position when at rest. In
larval and nymphal features this genus is then almost identical with Stegomyia.
Grabhamia. —Theobald has figured the larva of G. dorsalis. The antennæ
are distinctly of the Culex type, but the respiratory siphon is like that of a Stego-
myia. The figure is too small to allow of a full description.
Acartomyia. —Theobald's figure shows that the antennæ closely resemble
those of Stegomyia and differ only in having small spines scattered over them.
The respiratory siphon also possesses Stegomyia characters, being extremely
short. The trumpets of the nymph, on the other hand, appear to resemble those
in Howardina and Deinocerites (both in the sub-family Ædeomyina ).
Culex.—The species at present forming this genus are so numerous that
generalisations cannot be made on the result of the examination of a few species.
It appears from my researches that many of the species differ more widely in
their immature than in their adult stage. Certain species now classed under
Culex are, judging by larval characters, sufficiently distinct to be placed in
new genera, but we have not at present sufficient material to discuss this group
adequately, and, indeed, a proper division of the enormous genus Culex is impos-
sible until more is known of the immature stages of the species.
Provisionally, however, we may draw attention to several groups, which
from the dissimilarity of their larval characters alone, might well form separate
genera.
GROUP I. Culex (restricted sense). Culex (fatigans).—The ova are laid
8
so as to form rafts. The length of the raft is a little greater than the breadth.
The micropilar apparatus is "milled" laterally.
The larvæ are found especially in domestic utensils, pots, barrels full of
water, etc., and are rarely found in large masses of water or in water with
much vegetation.
The head is, rather large and quadrangular in shape. Some conspicuous
branched hairs arise from the dorsum. The clypeus carries two small thorn-like
spines, but no structures at all resembling clypeal hairs.
The antennæ are fully developed. The basal hairs and the median and
terminal spines are long and very noticeable. The first and second portions of
the antennæ form a straight line. The third portion is rather small. Small
spines are scattered over the first and the proximal part of the second portion
(Pl. II, fig. 13).
The siphon tube is distinctive ; .21 of body length. The siphonic index is
4.3. The spines number 6 or 7 in each row and extend over the lower third
of the tube (Pl. II, fig. 24).
The nymph of Culex fatigans has respiratory trumpets which project
laterally as shown in Pl. I, fig. 9. The opening calls to mind the obliquely-cut
mouthpiece of a penny whistle (Pl. I, fig. 7). This character, so far as my
researches have gone, appears to be peculiar to the restricted portion of genus
Culex we are discussing.
Specific variation.— A second species belonging to the restricted genus
Culex showed the following variation from the above.
C. ?. *—Larva found in wells and cement tanks. Antenna with the second
portion longer than in C. fatigans (Pl. II, fig. 14).
Siphon tube extremely large and conspicuous ; .28 of body length. Siphonic
index 4.1. Spines number 6 in each row and occupy the lower third of the
tube (Pl. II, fig. 25). Trumpets of nymph as in C. fatigans.
C. pipiens. —Theobald figures this species which clearly belongs to the
above group. The figure given is too small to allow of minute description, but
the antennæ are as in C. fatigans. The siphonic index 4.8. The siphon tube
similar in shape to C. fatigans.
GROUP II. C. impellens.—A group of mosquitoes of the original
genus Culex, possessing definite larval characters.
Antennæ as in Culex, but larger. Siphon tube more attenuated than in
C. fatigans. Siphonic index 6. Spines number 6 or more and extend over
basal one-third of tube (Pl. II, fig. 23).
Larvæ found more frequently away from habitations than are those of
C. fatigans.
* NOTE.—Identified by Mr. Theobald as C. fatigans, but evidently a distinct species.
9
GROUP III. Adult mosquitoes showing scale arrangement typical of the
genus Culex, but having larval characters recalling those of Stegomyia. Four
species, all unfortunately undetermined, were noted. All the forms were found
in natural pools.
Species a.—Nymph trumpets, opening wide, somewhat resembling those of
Stegomyia.
Head rather broad, antennæ like those of Stegomyia, but larger and having
a few small spines. Basal tufts small and composed of a few hairs. Median
and terminal spines abortive (Pl. II, fig. 7). Mental plate resembles that
of S. sugens (Pl. III, fig. 2). Siphon tube large (Pl. II, fig. 19), 18 of
body length. Siphonic index 1.9. Sixteen spines in each row shaped as in
Stegomyia.
Species b. —Nymph trumpet rather broad, but narrower than above. More
truncated than in species a. Antenna resembles that of Stegomyia (Pl. II,
fig. 8). Basal tuft small. Two rather large median spines present. No ter-
minal spines. The antennæ are covered with a few short spines.
Siphon tube large, . 2 of body length. Siphonic index 2.7. Eighteen spines
in each row.
Species c.—Trumpets of nymph nearly truncated, but opening slightly
obliquely (Pl. I, fig. 16).
Larva long. Rests in nearly vertical position (Pl. III, fig. 26). Head
very small and like that of Stegomyia. Antennæ comparatively small. Basal
tuft short, but composed of many hairs. Median and terminal spines small and
inconspicuous. Antenna covered with large and prominent spines (Pl. II,
fig. 9).
Siphon tube enormous and very massive, .26 of body length. Siphonic
index 5.9. Nineteen spines in each row. Whole tube strongly chitinised and
opaque (Pl. II, fig. 21).
Species d. —Trumpets of nymph resembling those of species c.
Larva long (Pl. I, fig. 22). Rests in nearly vertical position (Pl. III,
fig. 26). Head small and shaped much as in Stegomyia. Antennæ long and
well developed. Basal tuft short but composed of many hairs. Median spines
fairly well developed. Third portion of antenna readily seen. Terminal portions
short and inconspicuous. The whole antenna is densely covered with long
spines (Pl. II, fig. 10). Siphon tube enormous, not so massive as that of species c,
but very similar in its horn-like appearance, .28 of body of length. Siphonic
index 7.5 (Pl. II, fig. 22).
These larval characters certainly suggest that the group concerned have
little in common with the Culex fatigans group.
GROUP IV. Culex mimeticus. —Theobald figures the siphon tube and
C
10
I have been able to study the larva which occurs abundantly in the Nilgiris. The
larval characters have no relation to any other Culex larvæ. A curious point is
that the spines on the siphon tube, which is long and thin, are very large and
curved, thus differing from those of the great majority of larvæ which are short,
straight spikes.
GROUP V. C. concolor.—The larval characters of this species are quite
unlike those of any of the other groups. The larva of C. concolor is cannibal in
its habits and has the morphological characters of cannibal larvæ. ( Vide
description given later of cannibal larvæ.)
Theobald has figured parts of the larva of C. tigripes. It is evident from
his drawings that the larvæ of this species and that of C. concolor are very
similar. These two species alone amongst mosquitoes, of which the larva has
been described, possess the peculiar rudder-like group of hairs on the siphon.
Theobald, studying the adult insects, doubted whether they should be retained
in the genus Culex. If he has not already renamed these two species, I would
propose that they be placed in a new genus Jamesia, from the name of the
first describer of a cannibal larva (see also later).
Theobaldia.—The larva of Theobaldia annulata is figured by Theobald.
The characters are almost identical with those of C. fatigans
—
Ova laid in boat-shaped masses. The siphon tube as in C. fatigans.
Siphonic index 4. Antenna as in C. fatigans.
Melanoconion. —The ova of Melanoconion are laid in the form of rafts.
The rafts are more elongated than those of Culex. The individual ova resemble
those of Culex.
The larvæ of Melanoconion are peculiar and can be readily distinguished by
the naked eye (Pl. I, fig. 20). They resemble in general aspect the larvæ of
Tæniorhynchus and like these are often bright green and very transparent. From
the great development of the antennæ and hairs these larvæ have a " spiny "
look. They occur in clear natural water where there is much vegetation.
The head is widened transversely and is plentifully supplied with hairs.
There are two spines on the clypeus as in Culex. The mental plate is comb-
like (Pl. III, fig. 3).
The antennæ are extremely large and well developed. They form antler-
like projections which are very characteristic of the genus. The three portions
of the antennæ are very distinct, and the first may be curved. The hairs and
spines are all long and stout (Pl. II, fig. 15).
The hairs on the thorax are numerous and long. Immediately behind the
head two large hairs arise from papillæ near the middle line. These project
over the head and have already been mentioned as possibly being tactile in
function.
The siphon tube is long and very thin ; .23 of body length. The siphonic
index is 7. There are about 10 spines in each row which are rather long and
slender and extend over a little more than the basal third of the tube (Pl. II,
fig. 26).
The nymph of Melanoconion has distinctive respiratory trumpets. They are
peculiarly long and narrow and project in a more distinct curve than do those of
Culex. The end is more truncated than in Culex and the opening is on this
account more circular (Pl. I, figs. 8 and 10).
Tæniorhynchus.—The ova of Tæniorhynchus have been described by
Stephens and Christophers. 8 They are laid in the form of rafts which are
extremely long and narrow, and resemble in shape a racing skiff.
The larva is found in natural waters where much vegetation is present and
is often bright green in colour (P1. I, fig. 21 ).
The head is comparatively small. The clypeus is conical and so differs
from that of most larvæ. From the clypeus arise a few short, curved hairs. The
antennæ are well developed and resemble those of Culex. The basal portion
only is covered with spines (T. tenax, Pl. II, fig. 16).
The mental plate is highly characteristic, and was similar in two species.
It is triangular in shape and the two free edges carry very fine teeth which are
at least four times smaller than those of other. larvæ. The mental plate of
Tæniorhynchus has a remarkable resemblance to a shark's tooth (Pl. III, fig. 4).
The siphon-tube is peculiar, being extraordinarily long and thin (Pl. II,
fig. 27), .37 of body length. Siphonic index 12 . There are about seven spines
in each row confined to the basal tenth of the tube. The hairs arising from
the tube are very short and insignificant.
The nymph has respiratory trumpets which project anteriorly and nearly
meet in the middle line (Pl. I, fig . 11). The trumpets are large and pointed,
with an oblique opening (Pl. I, fig. 13). I have seen no other nymph in
which the trumpets project forward as they do in tæniorhynchus.
Mansonia.—The nymph of Mansonia uniformis has been figured by
Theobald. The trumpets appear to project forward as in the last-mentioned
genus.
Ædeomyina.— Of the large number of genera in this sub-family I am only
able to describe a very few, and those imperfectly.
Deinocerites.—Theobald has figured parts of the larva and pupa. The
siphon tube is large. The siphonic index (from Theobald's drawing) 5.6. The
nymph has abruptly truncated trumpets.
Howardina.—The nymph has somewhat conical and abruptly truncated
trumpets (PI. I, fig. 15).
Joblotia.—Theobald has figured the head and siphon tube of this larva. He
C 2
12
describes curious quadrangular frontal processes, but these appear to be the
widely opened maxillæ. The bodies he describes as antennæ are apparently
the maxillary palps. The siphon tube is very short and, from Theobald's drawing,
appears very unlike that of other larvæ.
Cannibal larvæ. —James 1 was the first to describe a species ( C. concolor)
in which the larvæ possessed cannibal habits. Theobald notes that the related
species C. tigripes is also cannibal. The larvæ of Megarhinus and Toxorhyn-
chites have been described by Theobald, and from the structure of their mouth
parts, are obviously also cannibal species. Lutzia and Psorophora, according to
Lutz,2 are actively cannibal. I have lately found the larva of Mucidus
scataphagoides to be cannibal and to possess the modified mouth parts which
appear to be characteristic of all these species. The following genera may be
noted as containing, and possibly consisting entirely of species having larvæ of
cannibal habits :—
Megarhinus.
Toxorhynchites.
Mucidus.
Psorophora.
Lutzia.
Jamesia
C. concolor.
C. tigripes.
(new genus).
In all cases in which the habits have been described in detail the larvæ are
characterised by their extreme voracity and their habit of preying solely upon
other mosquito larvæ. Although the species observed by us ( C. concolor and
M. scataphagoides) were seen to swallow small water-crustacea (Daphnia), yet
in the main they fed upon other larvæ. In both cases the larvæ lay horizontally,
quite motionless, with the modified brushes widely extended. When another larva
approached within a certain distance it was suddenly seized, no matter its size
or how vigorously it struggled. Small larvæ were often swallowed whole. Larger
specimens were devoured except the head-case and siphon tube. When food was
abundant, these larvæ increased in size with remarkable rapidity and ultimately
became conspicuous as giant larvæ. In Mian Mir both C. concolor and M.
scataphagoides were exceedingly common and were found wherever other Culex
larvæ abounded. The larvæ of M. scataphagoides occurred in pools with much
vegetation. C. concolor, on the other hand, was found together with C. fatigans
in pots, small dirty puddles, etc. In Mian Mir, and probably elsewhere, cannibal
species must play an important rôle in the reduction of the numbers of mosqui-
toes. From the examination of the two species already mentioned and from
Theobald's drawings of Megarhinus, Toxorhynchites, and C. tigripes, it is
13
evident that the larvæ of these genera are very similar in structure and appear-
ance. They all adopt a horizontal attitude. All have specially modified mouth
parts and possess conspicuous "clasping organs" in place of the feeding
brushes. The general appearance in all is similar ; the shape of the head and
clypeus is identical. The anal papillæ are rudimentary or absent.
Mucidus scataphagoides. —The full grown larva is very large, and its
horizontal attitude and the curious truncated appearance of the head are
characteristic.
The head is smooth and globular. Three long, conspicuous hairs arise on
each side. These differ from hairs in other larvæ in not being branched. The
clypeus overhangs the mouth and forms a curious concave edge, and not, as in
non-cannibal larvæ, a prominence. On each side of the clypeus a modified feed-
ing brush arises.
The feeding brushes are highly modified and form clasping organs. When
the larva is at rest, they project laterally as dark, horn-like structures. Each brush
is composed of a number of slightly curved chitinous bars, which have minute
comb-like projections on the concave side (Pl. III, fig. 14). The bars lie gene-
rally closely approximated, so that the clasping organ at first sight appears to
be composed of a single dense piece of chitin. The mental plate in both Muci-
dus and C. concolor is very similar and differs widely from that of any other larva
I have seen. In both species it carries only a few teeth, but these are of great
size (Pl. III, figs. sand 6). In Mucidus the maxillary palps are very small and
do not cover in the mandibles as in non-carnivorous species. The mandibles
are conspicuous, and the mandibular plate is very solid and massive.
The antennæ are small and resemble in general appearance those of
Stegomyia. The small basal tuft; however, rises very near the termination of
the antenna. The median and terminal spines are represented by a few
inconspicuous processes. There are a few small spines scattered over the
antenna (Pl. II, fig, 12).
The thorax is smooth and globular. The hairs arising from it and also
the hairs arising from the abdomen are simple and spring from well-marked and
chitinised papillæ. The siphon tube is long, the siphonic index being 4.6.
There are about 22 spines in each row and two conspicuous tufts of hairs above
these. There is no rudder-like fan of hairs rising from the median line as in
C. concolor and C. tigripes. The ninth segment differs from that of most larvæ
in possessing only rudimentary anal papillæ. The ventral fan of hairs has also a
more extended origin (Pl. III, fig. 16).
Megarhinus and Toxorhynchites. —The larva of T. speciosus figured by
Theobald corresponds in almost every detail with the above description. The
chief differences are in the presence of short, notched hairs arising from the
14
thorax of the larva of Toxorhynchites and the absence (?) of the spines of the
siphon tube in this species. Siphonic index is 2.5 (Pl III, figs. 12 and 19).
C. concolor. —In general appearance the larva exactly resembles that of
Mucidus. The antennæ and siphon-tube are, however, different. The antennæ
are small and very unlike those of any other larva (Pl. II, fig. 11). The siphon
tube is highly characteristic and possesses a structure not represented in any
other larva yet described (with the exception of the related species C. tigripes ).
This is a large fan of hairs springing from the median posterior line of the
siphon tube (Pl. III, figs. 17 and 18). The shape also of the siphon tube in
C. concolor and C. tigripes is quite unlike that of any other larva. The nymph
has respiratory trumpets differing from those of Culex. They project in a
characteristic way from the body of the nymph (Pl. I, figs. 14 and 23).
Psorophora. —From Howard's description of P. ciliata it is evident that the
larva is morphologically adapted for cannibal habits and resembles closely that
of Mucidus.
Lutzia. —The characters of this larva, so far as I am aware, have not been
described.
III.
From the above descriptions it will be seen that the most important varia-
tions occur on the following structures :—
1. The respiratory trumpet of the nymph.
2. The antenna of the larva.
3. The siphon tube of the larva.
4. The mental plate of the larva.
5. The feeding brushes of the larva.
6. The anal papillæ of the larva.
7. The form of the ovum.
8. The arrangement of ova in rafts or otherwise.
9. The form of the raft.
The shape of the nymph trumpets appears to vary little in species of the
same genus, but to be of great importance in the distinction of different genera.
By means of the variations on the trumpets the following groups may be
obtained.
1. Trumpets expanded to form a flap (Pl. I, figs. 1 and 2)
.
. Anophelina.
2. Trumpets expanded broadly triangular in shape (Pl. I, figs. 3, 4,
and 5)
Stegomyia.
Desvoidea.
3. Trumpets narrow with oblique opening (Pl. I, figs. 7 and 9)
. Culex.
4. Trumpets extremely long and narrow ; opening not so oblique
as above (Pl. I, figs. 8 and 10).
Melanoconion.
5. Trumpets project forwards (Pl. I, figs. 11 and 13)
.
.
.
Tæniorhynchus.
Mansonia.