EYE-SPOTS IN DIGENEA. IIQ 



eye at its best consisted of a pigment cup in which the contents 

 are figured but not recognized as lenticular in function. Monti- 

 celli's study (1914) of the eye structure in Cercaria echinocerca 

 Fil. is not as clear as the work of the earlier investigator on this 

 species. The eyes in Cercaria equitator (Ssinitzin, 1911: Fig. 54) 

 are of interest because they correspond to the X-type originally 

 described for the miracidium of Fasciola hepatica. Cort (1915) 

 discussed the eye-spots in monostome and amphistome cercarise 

 but failed to show their connection with the brain. 



MORPHOLOGY. 



The writer has studied intimately the eyes of several mono- 

 stome and distome cercariae (Faust, 1917, 1918, 19180). Of 

 twenty-eight species of cercarise which have come under the 

 writer's observation, seven possess pigmented eyes and four 

 have non-pigmented eyes. The existence of these non-pig- 

 mented eyes was first described by the writer for Cercaria race- 

 rnosa and C. graciUima (1917). 



The eye-spots of the binoculate species are usually in direct 

 connection w r ith the posterior dorsal nerve trunks (Faust, 1918). 

 However, the forked-tailed species, Cercaria gigas (Faust, 19180) 

 has connections with the anterior dorsal rami. While the 

 posterior dorsal trunks are, on the whole, much smaller and less 

 important than the corresponding ventral trunks, the ramus to 

 the lateral eye on each side is conspicuous. The cyclopean eye 

 in the trioculate species (confined to certain monostome cercariae) 

 arises from a fused anterior dorsal nerve trunk. It receives a 

 blunt nerve fiber from below. Thus it differs markedly from the 

 anterior pair of eye-spots in the M.onogenea which are innervated 

 by a branch of the same nerve which innervates the posterior 

 pair. 



Description of the eye-spot. In the pigmented eye-spots the 

 pigment consists of a cluster of rather large dark-brown granules, 

 grouped together so as to form a deep cup. At the base of the 

 cup the granules lie several layers deep, but toward the mouth 

 they are seldom more than one layer deep. The opening of the 

 cup in the case of the paired eyes is usually dorsolaterad, whereas 

 the cyclopean eye opens dorsomesad (Fig. i). Within the pigment 



