496 University of California Puhlicafions in Zoology [Vol. 18 



digestive system is that the mouth is located on the ventral surface 

 quite a little distance back of the anterior tip and not at the anterior 

 tip, as believed by other workers on this species. Ssinitzin (1909) 

 noted this same relation in the digestive system of Cercaria ocellata 

 La Valette, which is a schistosome cercaria of the group with eyespots. 

 His description and figures of the digestive system in this form 

 (Ssinitzin, 1909, p. 317, pi. 10, figs. 22, 23) agree almost exactly with 

 the description just given for the cercaria of /S'. japonicum. Miyagawa 

 (1916, pi. 4, fig. 30) notes the same rudimentary condition of the 

 esophagus and intestinal caeca in his studies on the cercaria of S. 

 japonicum.. He, however, considers that the mouth is at the anterior 

 tip, although he does not adequately describe or figure its relations 

 to the digestive tract in the oral sucker. Leiper (1915. fig. 2) figures 

 the intestinal caeca as very wide tubes extending to eaeh side of the 

 ventral sucker. The esophagus he shows to be very short. In fact, his 

 description and drawing of this structure are very different from 

 Miyagawa 's and my own. I believe that Leiper must have confused the 

 lobes of the nervous system with the digestive caeca, since he does not 

 show these structures. In view of Ssinitzin 's finding in Cercaria 

 ocellata and my own in the cercaria of S. japonicum, I would expect 

 to find such a rudimentary digestive tract as that described above in 

 all fully developed schistosome cercariae. 



ORAL SUCKER AND CEPHALIC GLANDS 



The oral sucker (figs. 1, 2) of the cercaria of S. japonicum is so 

 remarkably modified by adaptive larval characters that it has little 

 resemblance to the oral sucker of the adult into which it develops. It 

 has a length of more than one-third the length of the body, and has 

 distinctly separated anterior and posterior regions. In its anterior 

 region it is in direct contact with the cuticula. The layers of circular 

 and longitudinal muscle fibers of the body wall, which are strengthened 

 in this region, form its outer limits. The posterior region of the oral 

 sucker does not come into contact with the body wall, but is separated 

 from it by a considerable layer of parenchymatous tissue, and tapers 

 posteriorly in the shape of a blunted cone. This posterior region is 

 surrounded by a thick layer of circular muscles (figs. 1, 2, cm), the 

 fibers of which appear in the drawings in optical section. Within 

 the circular muscle layer is a thinner layer of longitudinal muscles. 

 The line of separation between the anterior and posterior regions of 



