414 FRESH-WATER BIOLOGY 



188 (187) Pigment in limited area near eyes. 



Cercaria diastropha Cort 1914. 



Smaller than last, eye spots larger in proportion. Pigment confined to 

 limited area near eyes. Tail always shorter than body. Genital organs dis- 

 tinctly marked out. 



Fig. 715. Cercaria diastropha, mature, dorsal view. Cystogenous glands not shown. 

 X 60. (After Cort.) 



189 (186) Cercariae grouped in btmches with individuals united by tips of 

 tails, which are very long and slender. 



Such forms, designated Rattenkonig- 

 cercarien by their discoverer, Leuckart, 

 are as rare as they are striking. C. 

 clausii from the marine fauna, the only 

 form of this type known previously, 

 was determined by Odhner to belong 

 to Phyllodistomum folium. The strik- 

 ing pecuharity in that the cercariae 

 are joined in groups is evidently not of 

 fundamental importance as the marine 

 form (C. clausii) and the species noted 

 here belong to different orders of trema- 

 todes. 



North American species. 

 Cercaria gorgonocephala 



Ward 1916. 



Fifty or more cercariae in a single 

 bunch. Tail, i.e., stalk, enlarged at 

 base with thick wall. Yellow pigment 

 in body. Stalk marked by two longi- 

 tudinal lines of dark pigment, attached 

 to postero-dorsal aspect of worm. 



Fig. 716. Cercaria gorgonocephala. Free- 

 hand sketch from life. X 40. (Original.) 



190 (i8s) 



Second sucker ventral, not at or near posterior end of body. 



Distome cercariae . . 



191 



Some distome cercariae are readily recognizable by characteristic features of adult struc- 

 ture like the collar and spines of the Echinostomidae which are as prominent in the cercaria 

 as in the adult, and apparently identical in form and arrangement. In the majority of cases, 

 however, the various groups of distome cercariae at present recognized are purely arbitrary 

 as they, are based on superficial characters. But the system cannot be rewritten until much 

 more is known of the origin of all of these larval organs and until a large number of species 

 has been studied. 



191 (247) Tail present in larva. 



The name Cercaria is applied strictlj 

 may be thrown off at an early period. 



192 (234) Tail not conspicuously modified in form or divided into regions. 193 



. . . . 192 



The name Cercaria is applied strictly only to such larvae as possess a tail, though the tail 

 may be thrown off at an early period. 



