Published Semi-Monthly at the Mew York Aquarium, cor. 35th Street and Broadway. 
VOL. 1. NEW YORK, WEDNESDAY, DEC. 6, 1876. NO. 5. 
ON SEA-SQUIRTS. 
BY PROF. ANDREW WILSON, M. D., EDINBURGH. 
Under the name of Sea-squirts curious beings 
may be found on all our coasts, attached to 
stones, to the broad fronds of tangle, and to 
other fixed objects at low-water mark. At first 
sight these creatures exhibit very little that is at- 
tiactive,' each organis m p r esenting, m - fec t , ttie f 
appearance of a soft, leathery-looking jar or bot¬ 
tle, with two necks or apertures. From this 
outward resemblance to a flagon, certain witty 
rhymes about “ leather bottles ” have been com¬ 
posed ; especially in allusion to the theory of 
some naturalists, that, in the young form of the 
Sea-squirt, man may trace his own ancient 
progenitor. 
The size of the more common species of 
Sea-squirts is never very great. From half an 
inch to an inch in length, may be regarded as 
fair average dimensions of these beings, which, 
in their outward aspect, as we have remarked, 
look like miniature jars, each fixed by the bot¬ 
tom to the rock, whilst two apertures exist on its 
upper surface. The body is encased within a 
tough outer skin, of leathery texture. And 
zoologists some years ago were very much sur¬ 
prised to find that, when chemically examined, 
this outer skin was composed almost wholly of a 
material named cellulose— a substance which till 
then had been regarded as solely confined to the 
plant-world. It is this cellulose which, in fact, 
forms the greater bulk of almost all vegetable 
tissues. It constitutes the walls of the delicate 
“ cells” of which plants are composed, and in 
its chemical nature closely resembles starch, 
which, as every one knows, is itself a notable 
product of plants. 
Naturally enough, this first item in Sea-squirt 
history excited much curiosity as to the cause of 
the manufacture, by the animal, ol a vegetable 
substance. But succeeding discoveries in the 
animal world revealed the occurrence of other 
examples of like phenomena. Thus the livers 
fcf quadrupeds are known to secrete a kind of 
animal-starch called glycogen, and other instances 
might be mentioned which serve to make the 
case of the Sea-squirts of no very exceptional 
kind in the modern zoologist’s opinion. 
Serving as a delicate inner lining to the tough, 
leathery coat of the Sea-squirt, we find a mem¬ 
brane, termed the “mantle.” This latter is 
composed of muscular fibres, and from the ac¬ 
tion of these fibres the Sea-squirts derive their 
familiar name. For, when touched or irritated, 
jets of water are squirted out from the two ori¬ 
fices of the bottle-like body, by the sharp con¬ 
traction of the muscular fibres of the mantle. 
One of these orifices — that placed on a higher 
level than the other — is the mouth ; the other 
may be named the atrial aperture, since it leads 
outwardly from a large sac, or chamber, known 
as the atrial sac. The resemblance of the Sea- 
squirt to the old wine-skin of Eastern nations, 
which was formed from the stomach of some 
animal, has given origin to their scientific name, 
Ascidians —the two orifices of the body roughly 
ASCIDIA PEDUNCULATA. 
corresponding to the two tied extremities of the 
wine-skin 
The internal structure of the Sea-squirts ex¬ 
hibits several features of rather curious kind, 
since in certain parts of their organization these 
molluscs differ from all other animals. The 
mouth thus leads into a large sac or bag, instead 
of into a throat as we might expect. The walls 
of this bag, which is the breathing-orgah of the 
Sea-squirts, are composed of a regular network 
of blood-vessels, the meshes of the network being 
fringed with numerous minute filaments, named 
cilia, the function of which is to keep up, by 
their constant waving, a continuous flow of wa¬ 
ter through the breathing sac. 
At the bottom of this sac the throat opens, 
and, as may readily be conceived, the situation 
of the throat admirably adapts it for the recep¬ 
tion of the particles of food that are drawn into 
the breathing chamber along with the copious 
currents of water, which contain the oxygen gas 
necessary for the purification of the blood. Thus 
there is a constant in-draught of water into the 
breathing sac, and it appears that the food parti¬ 
cles this water contains are strained off, so to 
speak, by paeans of numerous little grooves that 
exist in the floor of the sac, and which serve to 
guide the particles toward the throat; whilst a 
row of projecting feelers or tentacles, which line 
one side of the breathing chamber, may also aid 
in the latter function. 
But a most curious part of the life of the sea- 
squirt consists in the mechanism whereby the 
water which has been used in breathing — which 
has given up its oxygen to purify the blood, and 
its food particles to nourish the body — is got rid 
of to make way for a fresh supply. A second 
sac, named the atrial chamber, has already been 
mentioned as lying parallel with the breathing 
sac. Upon the atrial chamber devolves the duty 
of expelling the effete water of breathing ; and 
we may now see the use of the little filaments or 
cilia with which the breathing-chamber is so 
abundantly provided, and which thus by their 
constant motion create currents of water, flowing 
