196 , PROFESSOR HUXLEY ON THE ANATOMY 
membrane. The lower edge of the sac exhibits the same brown and undulating vessels 
as the back of the foregoing species, and ought in consequence to be regarded as the cor- 
responding region. The branchial cavity is very large ; it occupies those two-thirds of the 
tunic which lie nearest the circumference of the cylinder : its bottom, which is completely 
open, communicates freely with the other third, which lodges the viscera of the abdomen. 
These are small, and situated on the right side. The space which they leave unoccupied 
is commonly filled by the foetuses, which successively arrive and are developed there, as we 
shall see below. The structure of the branchial sac in the JByrosomata may lead one to 
believe that the water absorbed by the oral, makes its way out by the anal orifice. This 
would be a feature of resemblance with the Salpce, in which it is indubitable that the 
water takes this course. However this may be, the network which lines the cavity is 
otherwise organized : it is loose, and composed of fine, undulating, opake, white vessels, 
some of which are longitudinal, while others are transverse and cross the former at right 
angles — a character which is common to all the genera of this family. The network 
does not occupy the whole cavity, but only its two lateral walls ; so that there are obvi- 
ously, in this genus, two separate and opposite branchiae, one on the right and the other 
on the left, and which are much narrowed, and consequently distant, at the top. In 
the foregoing genera, the two branchiae, although really distinct, are only separate behind. 
The pharynx is at the bottom of the branchial cavity, towards its upper angle. The oeso- 
phagus is curved sharply to be inserted into a notch of the stomach, which is placed 
behind the bottom of the branchial cavity. The stomach is fleshy, smooth, compressed, 
ovoid, or slightly cordiform. The intestine, very delicate at its commencement, suddenly 
enlarges ; a short course brings it to the inferior edge of the tunic, where it receives 
the insertion* of a large organ analogous to the liver ; afterwards it returns to the stomach, 
behind which it ends in a simple and rounded anus. The feces are homogeneous, clear, 
yellow, and divided into little masses, the last of which is often already engaged in the 
atrial orifice (oscule anal), which seems to prove that the rectum has the power of elon- 
gating and of adapting itself to this orifice. 
" I must remark, that the liver, or the organ which from its position may be regarded 
as such, is attached to the intestine by a bundle of divergent canals ; that it is rounded, 
commonly opake, rose-coloured, yellow or brown, strangulated above its insertion, and 
divided into from eight to twelve ribs, by grooves which converge from its base to its 
apex ; it is very soft, and may be broken up into oblong pedunculated vesicles. I may 
add, as a remarkable fact, that, in many individuals, this organ is colourless, and that it 
resembles a cellular and transparent globule : it also varies greatly in volume ; some- 
times, and most frequently, it is of the size of the stomach, sometimes five or six times as 
large f . 
" The nervous system of the Pyrosomata does not appear to differ essentially from that of 
the foregoing animals. There are, in like manner, two tubercles, one on each side of the neck 
of the branchial sac. The anterior or superior tubercle seems to give off several filaments, 
An error : the organ in question being the testis. 
t Savigny has here clearly confounded the testis and the ovisac together under the one name of • foie.' What he 
calls the ribbed organ is the testis ; the cellular globule is an advanced ovisac. 
