MUSEUM OF COMPARATIVE ZOOLOGY. 



303 



not yet in communication with the stomach, and is still imperforated 

 at the anal end. The mouth (o) opens at the base of the branchial 

 sac, on the lucmal side of the posterior end of the gill («), and is joined 

 by a short curved oesophagus (o') to the stomach (o"); the intestine (o w ) 

 is parallel to the long axis of the stomach, and the anus {o"") is close 

 to the mouth, but opens, not into the branchial, but into the atrial 

 chamber, the posterior boundary of which is indicated by the line I. 



Fig. 5. 



~niu 



Nucleus of adult Cliain-salpa, — male; figured with the neural side uppermost : a, test ; b, 

 outer tunic ; 1, external aperture of testis ; 2, anus ; 3, mouth ; nu, nucleus. 



The whole digestive tract is immovable, and without muscles, and the 

 food is driven through the permanently distended cavity by means of 

 the cilia, with which its entire inner surface is lined. The great pos- 

 terior sinus surrounds the digestive system on all sides, and the 

 mitriment is absorbed directly from its surface by the blood. In the 

 young a layer of large dark-colored cells may be seen, covering the 

 posterior portion of the stomach and intestine (Fig. 33) ; these 



