EYE-SPOTS IN DIGENEA. 1 

 ERNEST CARROLL FAUST, PH.D., 



INTRODUCTION. 



While considerable work has been done on the eye structure of 

 the free-living Plathelminthes and ectoparasitic Trematoda, no 

 adequate study of the eye-spots of the digenetic Trematoda has 

 been made. In fact, although the nervous system of this group 

 has been comparatively well known since the days of Lang (1880), 

 students of Trematoda have been content with the mere mention 

 of the occurrence of eye-spots in this or that species, or at most 

 with a description of an isolated case and perhaps a reference to 

 this organ in Turbellaria or ectoparasitic Trematoda. 



There remain unanswered, then, two fundamental questions 

 relative to the eyes of Digenea, (i) What is the fundamental 

 structure of this organ, and (2) how extensive is the development 

 of the organ in the group. 



HISTORICAL. 



The earliest mention of eye-structure in Digenea was made by 

 O. F. M tiller (1773:68, 70) for Cercaria lemna. He suggested 

 that the two black pigment spots of these larvae were probably 

 eyes. Mehlis (1831) described for the first time pigment eyes 

 in miracidia (Cathemasia hians). In 1832 von Nordmann 

 (II., 140) made record of the eye-spots in the miracidia of Buno- 

 dera lucioperctz. Shortly afterward the X-type of pigment pat- 

 tern in the embryos of Fasciola hepatica and the two beehive 

 spots in the embryos of Cycloccelum mutabile were described. 

 Meanwhile other records of cercariae with eye-spots had been 

 published. O. F. M tiller in 1776 (C. inqiiieta), Hemprich und 

 Ehrenberg in 1831 (C. alata), J. Mtiller in 1850 (C. setifera and 

 C. elegant), and La Valette St. George in 1855 (C. ocellata) for 

 cercarise, and de Filippi in 1857 for the amphistomulum of 



1 Contributions from the Zoological Laboratory of the University of Illinois 

 no. 114. 



117 



