NO. 2286. THE NEW COPEPOD FAMILY SPHTRIIDAE— WILSON. 561 



lula it takes on more or less of an S curve. It opens into the stom- 

 ach at the anteroventral margin of the latter, the opening being sur- 

 rounded by a rather weak sphincter muscle. The mouth tube is not 

 sufficiently protrusible in any species of this family to affect the 

 esophagus at all. The stomach is abruptly enlarged behind the 

 sphincter and shows neither convolutions or processes in any of the 

 species examined. It is lined with digestive epithelium similar in 

 all respects to that found in other families. It passes insensibly 

 into the intestine which is rapidly narrowed into a mere thread on 

 entering the neck, and which shows neither convolutions nor fold- 

 ings. The intestine is widened again on emerging .from the neck, 

 passes nearer to the dorsal surface of the trunk, and is contracted 

 again into a relatively large and barrel-shaped rectum. The latter 

 evidently functions as an effective organ of respiration in devel- 

 opmental stages, and is operated by a set of dilator muscles on either 

 side. But after the development of the posterior processes this func- 

 tion is shifted to them, and although the rectum persists and in- 

 creases in size, it simply serves for the expulsion of the excreta. 



The intestine is smooth and unmodified in Paeon, but in Sphyrion 

 and Rebelula it becomes remarkably changed by the development of 

 lateral and dorsal processes. The wall of the intestine bulges out in 

 two rows of small knobs along either side, one dorsal and one ven- 

 tral, and one row along the center of the dorsal surface (fig. 30). 

 These knobs gradually elongate until the ends of those in the three 

 dorsal rows reach the dorsal wall of the trunk, against whose inner 

 surface they flatten out (fig. 31). The two ventrolateral rows grow 

 laterally more than ventrally, until they reach and flatten out against 

 the dorsoventral muscle strands. 



The inner cavity of all the processes remains in full communica- 

 tion with the lumen of the intestine. The dorsolateral processes 

 reach the dorsal wall of the trunk just inside of the dorsoventral 

 muscles, while the dorsocentral processes flatten out between the lon- 

 gitudinal bands of muscle. 



Subsequently in Sphyrion all the processes elongate laterally until 

 on the dorsal surface they fill almost the entire median space between 

 the two sets of dorsoventral muscles, with only a very narrow sinus 

 on either side beneath the longitudinal muscles and between the cen- 

 tral and the lateral row. On the ventral side they crowd out into 

 the dorsoventral muscles and grow inward around the intestine, 

 until they almost meet on the midline, presenting the appearance 

 seen in figure 32. 



The intestine, together with these five rows of processes, fills prac- 

 tically all the lumen of the trunk between the dorsoventral muscles, 

 the only vacant space being below the center of the intpstine, be- 



