56 ANATOMY AND PHYSIOLOGY OF SALPA AND PYROSOMA 



than an aggregation of clear circular cells about v^yth of an inch in 

 diameter (8). These were considered by Savigny to be the ovaria, 

 but they have not the appropriate structure, and it will be seen that 

 the ova are formed elsewhere. 



In all the rest of their extent the inner and outer tunics are 

 separated by a very obvious space. This is one large vascular sinus, 

 and the viscera lie in it and are bathed by the blood which fills it. 



The heart (^) is placed on the dorsal side just behind the posterior 

 extremity of the internal shell. In structure it perfectly resembles 

 that of Salpa, and its contractions are reversed in a similar manner. 

 No distinct vessels were to be traced in these animals. 



49. The endostyle (r) resembles that of Salp(X in its structure. It is 

 as long as the branchial chamber, and lies in the dorsal sinus, sup- 

 ported by a projecting ridge of the inner tunic. On each side of it 

 below, there is a longitudinal thickening, which readily gives rise to 

 the appearance of four dorsal bands or " undulated vessels," described 

 by Savigny. 



50. The branchiae izi) are symmetrical, one on each side, and are 

 composed of a network formed by longitudinal and vertical bars or 

 lamina. 



The vertical bars are outside ; the longitudinal bars are at equal 

 distances along their inner surface, and are attached at the point of 

 intersection. 



The vertical bars are attached to the inner tunic at their upper and 

 lower extremities ; for the rest of their extent they are free. 



The longitudinal bars (f, fig. 3) are rather lamina, flattened horizon- 

 tally, slightly thickened at their free edges, and beset along the upper 

 surface of these edges with small teeth ; they project anteriorly and 

 posteriorly beyond the vertical bars. 



Both systems of bars appeared to be tubular, although no corpuscles 

 were seen moving in them, and the edges of the vertical sinus were 

 thickly covered with long cilia, moving in opposite directions on the 

 opposite sides. 



5 I. The dorsal edges of the two branchiae were separated by a space 

 containing the thickened dorsal folds already mentioned, and this is 

 continuous posteriorly with a band which connects the mouth with 

 the dorsal surface of the respiratory cavity, and allows the water to 

 pass back on each side of it to the post-branchial cavity. 



52. Anteriorly on the ventral side is an organ (fig. 10 ic) analogous 

 to the " ciliated fossa " of the SalpcB, and behind this a series of 

 tongue-shaped eminences (fig. i /) projects into the respiratory cavity, 

 analogous to the " languet " of the Salpce. 



