Year: 1872

cations.


The following interesting letter,
written by Professor Agassiz on
board the coast-survey steamer dass-
ler, has been received by Professor
Benjamin Pierce, superintendent OF
the coast-surveJ


ST.. THOMAS, Dec. Is, 1871.
Ny Dear Professor:-For several
days after we left Boston was great
ly troubled by a sense of general
weakness, so much so that more than
once | thought 1 had undertaken
more than | had strength for. But
as soon as we got into warmer lati-
tudes L felt better, and now [ am
actually improving beyond my con-
dition at the start. As soon as we
reached the Gulf Stream we began
work, Indeed Pourtales organized q
party to study the temperatures as
soon as we passed Gay Head, and he
will himself report his results to
you, which are quite interesting.
My attention was entirely turned to
the gulf weed and its Inhabitants, OF
which we made extensive collec-
tions. Our observations favor the
views of those who believe that the
floating weed is derived from plants
torn from the rocks upon which sar-
gassum naturally grows. Imsce .
very simple experiment which seems
te me to settle the matter. Every
branch of the sea-weed which is de-
priyed of its floats at once sinks to
the bottom Of the water, and these
fioats are not likely to be the first
parts developed from the spores.
Moreover, after examing a very large
quantity of the weed, 1 can say that
l have not seen a branch however
small which did not exhibit distinct
marks of having been torn from a
solid attachment


You may hardly feel an interest in
my zoolog oal o5,erva'i ons, but am
sure you viii be pleased to learn that
we had the best opportunity of care
fully examining most of the animals
known to inhabit the gulf-weed, and
some which did not know to occur
among them. However, the most
interesting discovery of the voyage
thus far is the finding of nest built
by fish, floating on the broad ocean
with is live freight. On the 18th of
the month Mr.. Mansfield, one of the
officers of the Hassler, brought me
ball of gulf-weed which he had just
picked up, and which excited my Gu
riosity to the utmost. 1t was q round
mass of sargassum, about tine size of
two fists, rolled up together. The
whole consisted to all appearance of
nothing bat gulf-weed, the branches
and leaves Of which were, however,
evidently knit together and not only
balled into roundish mass, for
though soma of the leaves and
branches hung loose from the rest, it
became at once visible that the bulk
of the bail was held together by
threads trending in every direction
among the sea-weeds, as if a couple
of handfuIs of branches of sargas-
sum had been rolled up together
with elastic threads trending in every
direction. Put back into q large
bowl Of water it became apparent
that this mass of sea-weeds was a
nest, the central part of which was
more closely bound up together in
the form OF ball with several loose
branches extendingsin various direc-
tions, by which the whole was kept
floating.


a more careful examination re-
vealed the fact that the elastic threads
which held the guIfweed together
were beaded at intervals, sometimes
two or three beads being close to-
gether, or bunch of them hanging
from the same cluster of threads, or
they weTc more rarely scattered at
greater distance one from the other.
Nowhere wa, there much regularity
observable in the distribution Of the
beads and they were iound scattered
throughout the whole ball of sea-
weeds pretty uniformly. The beads
themselves were about the size of an
ordinary pins head. We had, no
doubt, q nest before rs of the most
curiou. kind, full Of eggs too, and the
eggs sc.ttcred throughout the mass
of the nest and placed together in q
cavity Of the whole structure.


What animal could have built this
singular nest, was the next question.
Il did not take much time to ascer-
tain the class of the animal kingdom
to which it belongs. A common
pocket lens at once revealed two
large eyes upon the side of the head
and a tail bent over the back of
the body, "a the embryo uniformly
appears in ordinary fishes shortly be-
fore !he period ofhatching. The many
empty egg cases observed in the nest
gave promise ofan early opportunity
of seeing some embryos freeing
themselves from thsir envelope.
Means hile a number of these eggs
with 1.-Two ombryOs were cut out ofthe
ncst and placed in separate glass Jars
to multiply the chances of preserv-
ing them, while the nest as q whole
was secured in alcohol as a memorial
OF our unexpecte d discovery.


The next day found two embry os
in one Of my glass jars they occa-
siouully moved in jerks and then
rested Cor a long while motion
less upon the bottom of the jar. On
the third day | had over dozen of
these young fishes in my rack, the
oldest of which begin to be more
active and promise TO afford further
opportunity for study. l need not
relate in details the evidences soon
obeaiGed that these embryos were
fishes. Suffice it to say that the
dOrsal cord with its heterocercal
bent was readily visible, as well as
the Caudal fin with its rays. In the
eyes the coloboma had not yet been
fully closed, and blood currents were
unmis'.kaJle on the yolk bag. But
what kiai OF fish vas this? About
tho time of hatching the fms of this
Glass OF animals differ too much from
those of the adult, and the general
form exhibits too few peculiarities,
TO afford any clew to this problem.
couldionly suppose that it would like
ly prove to be one of the pelagic spe-
ciGs of the Atlantic, and of these the
most common are exocoetus, naucra-
tee, scopelus, chironectes, syngnethus,
moaacanthus. tetraodon, and dioden.
/, Was there way to come nearer to a
correct solution Of my doubts?


As L had in former years made a
somewhat extensive study of the
pigment cells of the skin in g variety
OF young fishes, L now resorted to
this method to identify my embrYOs.
Happily we had on board several
pelagic fishes aiive. which could af-