56 



lts walls are usually thinner at each of its lateral edges than elsewhere (PI. XI, fig. 126), 

 indicating the power of dilating and contracting in a definite way. lts posterior aperture commonly 

 projects into the stomach in the manner shewn in figs. 34, 42 (PI. IV). 



The stomach has high, glandular walls which are almost certainly pigmented. The 

 epithelium is usually not well preserved. The shape of the cavity is complicated by numerous 

 folds, which in entire zooids, both of C. dodecalophis and of C. levinseni^ are seen to be arranged 

 principally in the frontal direction. This may indicate that they are partly due to the general 

 contraction of the body-musculature. 



The second stomach, which opens from the main organ, has an epithelium which 

 appears to be glandular, and is considerably higher than that of the succeeding part of the 

 canal. It may be presumed that digestion is continued in this part. 



The i n t e s t i n e may be considered to begin at the point where the coelom which 

 extends between the two limbs of the f'^shaped loop of the alimentary canal ends (figs. 34, 37). 

 lts relatively thin walls pass continuously into the higher epithelium of the second stomach on 

 the one hand and into those of the rectum on the other hand. The rectum is merely a 

 part of the intestine, with which it is perfectly continuous, but the name may conveniently be 

 employed for the last part of the alimentary canal, the dorsal wall of which is exposed to the 

 third body-cavity. The size and shape of the rectum differ according to the state of contraction 

 and the development of other organs. Thus in fig. 42 the small lumen seen in the rectum 

 appears to be due to the specially large size of the ovary. 



The food of Cephalodiscus seems to consist principally of microscopic organisms. The 

 cell-walls of Diatoms are found in various parts of the alimentary canal, with other detritus, 

 among which Sponge-spicules can often be recognised. But in addition to the smaller particles, 

 larger organisms are occasionally found. Thus a considerable part of the intestine and rectum 

 of the individual of C. levinseni shewn in fig. 33 is occupied by an organism which seems to 

 be a Copepod in a partially digested condition. I have found a similai- case in a specimen of 

 C. dodccalopJuLs, while the individual of this species shewn in figs. 152 — 155 has in its stomach 

 what appears to be a Polychaet, some of the long cirri of which are imbedded in the digestive 

 epithelium. I am inclined to regard this as a case of parasitism. 



Mouth, Pharynx and Notochord. 



The study of the commencement of the alimentary canal is of special importance in 

 conne.\ion with various physiological problems, and specially in the consideration of the probable 

 mode of feeding. As in the case of several other parts of the animal, it is by no means easy 

 to distinguish between temporary folds due to contraction and grooves or ridges which are 

 permanent, and of morphological or physiological importance; while the varying positions assumed 

 by the jjroboscis-stalk, the arms and the operculum introducé further difficulties in interpreting 

 the structure of the mouth. 



