PEROPHORA ANNECTENS. 63 



organ fail to adequate!}' represent the differentiation of it 

 into the well-defined sections that actually exist in it. 



I had thought, before having an opportunity to examine 

 any of the other species, that since none of the descriptions 

 or figures of the organ under consideration show in any but 

 a most indistinct and partial way several features that are 

 quite obvious in this species, that perhaps a considerable 

 difference existed here between this and the other species. 

 As, however, I find on examining P. viridis that essentially 

 the same structure here obtains, it is quite certain such is 

 likewise the case throughout the genus. Fig. 9, pi. i, 

 represents the digestive tract as it appears when dissected 

 from the animal and examined in toto. There are five 

 quite distinct regions to be recognized, instead of three, 

 as described by R. Hertwig ('72, p. 90), and many other 

 writers, for many tunicates. Whether these all cor- 

 respond, both morphologically and physiologically, to the 

 five regions described by Milne-Edwards ('42, p. 275), 

 in the same organ in Clavelina, I am not sure; neverthe- 

 less, I use his terms to designate them. These are: a-., 

 oesophagus; s/., stomach; //;/.' duodenum; int." intest- 

 ine consisting of: cli. v., the chylific vesicle, and re, the 

 rectum. 



Maurice ('88) finds five regions in the digestive tract 

 of Fragroides, to which he also applies the same terms. 

 The oesophagus is short and wide, and there is no valvu- 

 lar constriction at its entrance into the stomach, as is the 

 case in some tunicates. At the passage from the stomach 

 into the duodenum there is a pronounced constriction, and 

 the narrow proximal end of the duodenum is thrust into 

 the much wider stomach, to which it is joined so that a 

 pronounced lip, or fold is formed around the orifice. This 

 structure is readily understood by reference to fig. 22, pi. 

 iii, which represents a nearly longitudinal section through 



