44 PELONAIADiE. 



them on each side they are very prominent, and are tied each by 

 a minute cord to the inner surface of the mantle. The internal 

 surface of the sac exhibits along one side the serpentine double 

 cord which contains the branchial vein ; along the other side the 

 branchial artery; and from these primary and secondary perpen- 

 dicular branches proceed, as in the other Ascidice. The trans- 

 verse plaits on the external surface of the sac correspond to the 

 primary or tranverse branches of the vessels on the internal sur- 

 face. The animal was not examined while alive, but cilia, without 

 doubt, exist in great abundance on the edges of the lozenge-shaped 

 spaces of the sac. 



" The cesophagus commences by a white plicated opening at the 

 lower end, and on one side of the sac. It is curved in a sigmoidal 

 form, and exhibits longitudinal rug?e through its coats. Near 

 the lower end of the mantle-cavity it terminates by suddenly di- 

 lating into the stomach, which is pear-shaped, and directed ob- 

 liquely upwards towards the side opposite to the cesophagus. The 

 internal surface of the stomach presents longitudinal plicae, and 

 is succeeded by the intestine, which at first curves upward, then 

 down to the bottom of the mantle cavity, up along the oesopha- 

 geal side of that cavity, and between its walls and the branchial 

 artery, terminating about the anterior third of the animal in a 

 funnel-shaped anus, which is cut into ten or eleven processes, like 

 the petals of a flower. The first part of the intestine is white and 

 longitudinally plicated ; the rectum is dilated with attenuated 

 coats. 



" 3. Vascular System. — The vascular system resembles that of 

 the true Ascidice, except that there is no heart. It consists of two 

 sets of vessels, with four sets of capillaries, a circle in fact twice 

 interrupted, once in the respiratory sac, and again throughout the 

 body. The branchial veins run along the transverse plaits of the 

 sac, receiving secondary and ternary twigs at right angles. The 

 primary branchial venous branches empty themselves on each side 

 into the branchial trunk, which runs in the substance of the 

 double cord which coasts the superior aspect of the sac. This 

 double cord terminates in an abrupt manner anteriorly near the 

 oral orifice, and in a similar manner, but after becoming smaller 

 near the orifice leading to the oesophagus. At this point the vein 

 becomes an artery, and probably sends back vessels to nourish the 



