513] LARVAL TREMATODES—CORT 67 



present in very young forms, but cast off before 

 encystment, which takes place within the sausage- 

 shaped sporocysts. Ex. Cercaria of Lepodora 

 rachiaea. (?) 

 b. Cercariae developed in rediae. 



(1) Cercariae neptuneae 



Tail very thick and large, two eye-spots present. 

 Excretory vesicle very thick walled. Ex. Cer- 

 caria neptuneae Lebour. 



(2) Acanthopsolus group 



Two eye-spots, intestinal ceca reaching nearly 

 to the end of the body, thin tail developed in 

 young forms but cast off before it is full grown. 

 Ex. Cercaria of Acanthopsolus lageniformis. (?) 



(3) Echinostomum group 



Cercariae with anterior collar and crown of 

 spines. Ex. Cercaria trivolvis Cort. 

 2. Monostome group 



One sucker present. Ex. Cercaria urbanensis Cort. 



It is in attempts to join a few closely related cercariae into groups 

 which are probably natural, rather than in further broad generalizations 

 which must be based on artificial characters, that hope for advance in 

 the classification of cercariae lies. As more and more life-histories are 

 worked out, such groups can be fitted into their place in the adult classi- 

 fication, until the relationship of all the cercariae groups to the adults 

 will be known. 



Note. All of the species of Cercaria discussed in detail in this paper were 

 originally described in my preliminary report (Cort, 1914). 



