124 ERNEST CARROLL FAUST. 



(1911) and Faust (1917); for furcocercous forms by La Valette 

 (1855), Sonsino (1897), Cort (1914, 1917), O'Roke (1917) and 

 Faust (1917, 19180); and, in addition, for many other less closely 

 related species by O. F. M tiller (1773, 1776), Hemprich und 

 Ehrenberg (1831) and Ssinitzin (1911). Holostome cercarise 

 have not been shown to possess pigment eye-spots. The exis- 

 tence of the cercaria stage in Aspidocotylea is still uncertain. 



After the cercaria stage the pigment may persist for a little 

 while but is usually lost on the arrival of the fluke within the 

 definitive host. However, the pigment granules persist in some 

 cases, being found in the mature worm. Although the pigmen- 

 tation of the monostome cercaria is carried over to the encysted 

 monostomulum, pigmentation in adult monostomes is quite 

 unknown. On the other hand, several amphistomula which 

 have reached their final host still have a clump of pigment 

 granules around the optic end organ. Among distomes the dis- 

 tomula and adults known to possess pigment eye-spots belong 

 to the Allocreadiidae or closely related species. In many cases 

 the pigmentation is faint and the "lens" degenerate. No holos- 

 tome adults are recorded as having pigmented eyes. Whereas 

 the other stages in the life cycle of the Aspidocotylea are in 

 doubt, the group is represented in the adult stage by one pig- 

 mented species, Cotylaspis insignis. 



Reviewing the entire field of the Digenea, pigment eye-spots 

 are found in representative species of all suborders of the 

 Prostomata at one time or another in the life cycle of the 

 individual. Among the monostomes, both miracidia and cer- 

 carise commonly possess these organs. Amphistome miracidia 

 usually lack pigment eyes, while amphistome cercarise are 

 usually binoculate. Holostome miracidia are pigmented (at 

 least in one species), while neither cercariae nor adults are pig- 

 mented. Few distome miracidia are marked by pigment eye- 

 spots, although a pigmented optic organ is common in cercarise 

 of various distome families and usually present in Allocreadiide 

 distomulaand adults. The only recorded instance of pigmented 

 eye-spots in miracidia, cercarise, and adults is that of Bunodera 

 lucioperccB. 



