o'roke: larval trematodes. 175 



In all cases where this form was found, the infection was heavy, 

 the liver of the snail being filled with almost a solid mass of the 

 sporocysts. Estimates of the numbers of cercarise emerging from 

 any one snail ran from five thousand to eight thousand. 



Notes. 



The following notes, while adding little to this paper, might be 

 of assistance to any one wishing to work out life histories of 

 trematodes. 



The collecting grounds from which my material was taken cov- 

 ered a wide range of habitats, from temporary pools and pasture 

 streams to artificial ponds and permanent lakes. 



Onl}^ two genera of snails were examined. Infection was very 

 rarely found in young snails, and never in snails collected from 

 temporary pools or pasture streams. Old ponds harboring fish, 

 frogs, muskrats and water snakes usually contained infected 

 snails. 



All of the fm'cocercous cercarias were found in Physa collected 

 from muddy permanent ponds. The large amphistome cercarias 

 and the xyphidio cercarise were found in the genus Planorbis in 

 the larger, clearer lakes. Lakes of this type are inhabited by the 

 species of water life mentioned for the other type of ponds, and 

 in addition are frequented by migratory birds. 



The heaviest infection was found the latter part of August at 

 the State Fish Hatchery at Pratt, Kan., where the number of 

 snails parasitized ran as high as 90 per cent. 



Only one of the species studied, Cercaria cortii, encysted under 

 observation, and no cysts of any of the other forms were found 

 outside of the snail. 



One specimen of Planorbis trivolvis, collected from pond No. 5, 

 July 24, showed the presence in the digestive gland of large num- 

 bers of spherical cysts about .05 mm. in diameter. These cysts 

 correspond to those of Cercaria trivolvis described by Cort as 

 having been found in the body cavity of Planorbis trivolvis. 



One characteristic of Cercaria gregaria possibly throws some 

 light on the life history of the species. This is the peculiar habit 

 that the cercarise have of losing their tails and forming compact 

 masses in the water, each mass containing from fifty to five hun- 

 dred individuals. 



