48 ILLINOIS BIOLOGICAL MONOGRAPHS [494 



were represented several infections and that the approach of winter, 

 for the examinations were made in November, may have arrested the 

 development of the second brood. 



The only possible group in Liihe's (1909) classification of the cer- 

 cariae where Cercaria trigonura might fit is with the Microcercous cer- 

 cariae. An analysis of the forms coming under this category shows that 

 they cannot form a natural group. Dollfuss (1914) in the preliminary 

 account of his work on this group separates from it the Cotylocercous 

 cercariae which he considers to be a natural subdivision. 



He gives the following characters for the Cotylocercous cercariae. 



1. Cercariae developing in simple sporocysts parasitic in marine 

 gastropods. 



2. Oral sucker with stylet ; stylet glands fill a large part of the 

 anterior region of the body. 



3. Bladder large not bifurcate occupying almost all the posterior 

 region of the body; wall formed by a single layer of large granular 

 cells, which have the appearance of glands. 



4. Tail very short, wide at least at its base, consisting of a cup with 

 thick walls of large cells, which functions as a sucker. 



Dollfuss is in doubt in regard to the specific distinctness of some 

 of the members of this group. He therefore designates them together 

 provisionally under the name Cercaria pachycerca Diesing "sensu lato 

 et var. ' ' Under this designation he includes Cercaria brachyura Lespes, 

 Cercaria cotylura Pagenstecker, and several new forms. Besides these 

 are included in the Cotylocercous cercariae as undoubtedly distinct 

 species Cercaria linearis Lespes and Cercaria buccini sp. inq. Lebour. 

 Dollfuss states in regard to this group that the cercariae are so alike 

 in structure that the adults must be closely related. 



Aside from the cercaria of Catoptroides macrocotyle Liihe (Phyllo- 

 distomum folium Ssinitzinj and metacercariae, which have been related 

 to the Microcercous cercariae without any good reason, there are left 

 after the separation of the Cotylocercous cercariae, five more or less well 

 known forms. 



1. Cercaria limacis (Moulinie' (1856:83, 163-164) from sporo- 

 cysts in the terrestrial molluses Arion rufus L. and Limax cinereus 0. F. 

 Miiller. 



2. Cercaria micrura de Filippi (1857:5-7) (larva of Sphaerosto- 

 mum bramae (0. F. Miiller) from sporocysts in the freshwater snail 

 Bithynia tentacidata. 



3. Cercaria myzura Pagenstecher ( 1881 :25 f -26 ) from rediae in the 

 fresh-water mollucs Neritina (Theodofda) fluvialme- L. 



