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 

 shaU see below. The structure of the branchial sac in the Pyrosomata may lead one to 

 believe that the water absorbed l^y the oral, makes its way out by the anal orifice. This 

 would be a feature of resemblance with the Sal'pce, in which it is indubitalile 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 retmms to the stomach, 

 behind which it ends in a simple and rounded anus. The faeces are homogeneous, clear, 

 yellow, and divided into little masses, the last of which is often already engaged in the 

 atrial orifice {pscule 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 t. 



" The nervous system of the Fyrosomata 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 oflF 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. 



