340 



THE AMERICAN NATURALIST 



[Vol. LII 



nary killing fluids. This lias resulted in my not being 

 able to secure suitable sections for detailed study. It 

 will probably be necessary to make most of the observa- 

 tions upon living material, which will require that one 

 have a microscope and microscopic reagents while doing 

 field work. 



The following general facts may help to direct atten- 

 tion to this important stage in the development of the 

 life history of Trematodes. Possibly some fish contain- 

 ing them may be found near a laboratory and thus readily 

 studied. 



Fig. 4 shows the usual position of these larval stages 

 in the muscles of the long-eared pumpkin seed taken in 

 Lake Clear during July, 1915. Each cyst is accompanied 

 by a small amount of pigment in the more advanced 

 stages, although I have seen many of them with no pig- 

 ment and nearly the same appearance as the muscle (Fig. 

 7). One must often pick the muscle fibers apart in order 

 to find the cyst as most of them do not show on the sur- 

 face. I have not been able to discover that they are 

 found in any definite region of the body, although they 

 are more numerous near the dorsal fin. 



A photomicrograph of a young cyst shows a number 

 of blood vessels entering one end of the cyst. The cyst 



