EYE-SPOTS IN DIGENEA. 123 



increased activity. The pigment is possibly both light- and heat- 

 percipient. 



DISTRIBUTION OF PIGMENT IN THE DIGENEA. 



For convenience the pigment spots in miracidia, cercariae, 

 immature and mature trematodes will be discussed separately. 

 Leuckart (1886: 73) states that in general eyes are lacking in 

 miracidia, while Ward (1918) defines a miracidium as possessing 

 an eye-spot. In treating the nervous system of Digenea, Braun 

 (1892) remarks that pigment eyes in adults are exceptional, 

 citing Acanthopsolus ocellatus (Levinsen) as the only adult in 

 this order in which eye-spots are known. A survey of the group 

 shows that the data are isolated and in many cases incomplete. 



The common examples usually cited in miracidia are the bee- 

 hive pigment eyes of Cycloccdum mutabile and the X-type of 

 Fasciola hepatica. Among monostomes it is the common thing 

 to find pigment flecks in the ciliated larva, even in the eggs in 

 ntero. Among distomes the only species found with pigmented 

 eyes in miracidia are Fasciola hepatica, F. hepatica var. agyptiaca, 

 Bunodera luciopercce, and Cathemasia hians (fide Leuckart). 

 The miracidium of the holostome, Strigea cornucopia (von Lin- 

 stow, 1885) possesses conspicuous eye-spots. No record of pig- 

 ment spots in the miracidia of amphistomes has been found, 

 although Looss (1892, 1896) has worked out the details in the 

 early stages of the life history of four representative species. 

 The miracidia of the Aspidocotylea are not well known. 



No pigment eye-spots have been described for the parthenitae. 



Turning to the cercariae, one is struck by the disproportionally 

 wide distribution of pigmented eyes. In monostomes the cer- 

 cariae thus far described possess eye-spots of the binoculate or 

 trioculate types (Fig. i). Amphistome cercariae are commonly 

 binoculate. Both monostome and amphistome cercariae have a 

 considerable amount of pigmentation over the nerve center around 

 the eyes. However, the greatest number of records of eyes in 

 cercariae concerns the distomes. They are recorded for gym- 

 nocephalous species by Ercolani (1881 : 54, 55), and Looss (1896: 

 "204-210); for setiferous species by La Valette (1855), Odhner 

 (1914) and de Filippi (1857: 433); for stylet cercariae by Ssinitzin 



