4Q6 HARRY M. MILLER, JR., AND FLORA E. NORTHUP. 



TABLE I. -(Continued). 



would play a considerable part. There are no data in Dimon's 

 (1905) study of the biology of Nassa obsoleta on the life span of 

 this species, nor whether large numbers die at any particular 

 season of the year. The question of age immunity does not 

 enter into the present study, as only data for large specimens of 

 Nassa were included in the graphs; one collection of small 

 individuals showed an infestation of only 0.7 per cent, on August 

 15, 1925, in contrast to 2.4 per cent. (Aug. 6) and 1.4 per cent. 

 (Aug. 1 8) for two collections of large ones. 



Inspection of the grapn for emerged cercarinea (Text-fig. 2) 

 shows that in the different collections there is variation in the 

 percentage of snails harboring mature larvae. There does not 

 seem to be any correlation between these percentages and the 



2 Small snails; data not included in any graph. 



