Occasional Papers of the Museum of Zoology 9 



in association with still smaller numbers of Ccrcaria iiiarcianae. 

 The cysts enclosing individuals of C. vegrandis diilered in the 

 two host species. In T. cqucs the cyst membrane was tough, 

 moderately thick and the enclosed cercaria was released with 

 difficulty while in T. marciana the cysts were scarcely dis- 

 cernible, the cercaria were released with ease, almost as readily 

 as C. marcianae were released. The cysts in T. uiarciana al- 

 ways ruptured without being torn from the fat body. This 

 difference in the response of closely allied host species to the 

 presence of the same parasitic species is rather remarkable. 



Type: jNIuseum of Zoology, University of ^^lichigan, slide 

 ^^- 155 J paratypes alcoholic material in collection of the 

 Aluseum, slides and alcoholic material in the collection of the 

 writer. 



Description: The study of this species is based entirely on 

 preserved specimens removed from fat bodies. Such speci- 

 mens were frequently so rolled or twisted that they could not 

 be studied while others were ovate in form, being sometimes 

 very broadly ovate, the greatest breadth occurring near the 

 middle or near the posterior end. Alore rarely the specimens 

 are somewhat slender (Fig. 3). No specimens have either one 

 or both ends acute. Rarely an elliptical form was assumed. 

 They were in all cases very flat and tailless. The parenchyma 

 •differs greatly from that found in C. inarcianac, being filled 

 with small round or oval cavities measuring about o.oio X 

 o.oio or O.OIO X 0.012 mm. These are best seen in unstained 

 but cleared specimens. Nuclei are numerous. In all speci- 

 mens studied, about twenty, the parenchyma which was 

 opaque masked the details of various structures to such an 

 extent as to make their study difficult and in some cases im- 

 possible. 



