TREMATODE SPOROCYSTS AND CERCARI^. 



199 



collecting will give details of frequency of occurrence with such 

 other observations as seem to be appropriate. 



1909- July 3, 34 snails examined, no parasites found. 



July 19, no snails examined, 21 sporocysts found. The 

 sporocysts were inactive and contained tailless cercariae which 

 were very active. So far as examined the sporocysts in this lot 



Fig. I. Sporocyst containing cercariae, from Ilyanassa obcoleta: in sea water 

 flattened under cover glass. Length 0.86 millimeter. 



contained relatively few cercarise, 9 being the greatest number 

 seen, and as few as 2 noted in one sporocyst. 



Three sporocysts lying free in sea water had the following 

 dimensions in millimeters: 



Length 0.62 0.75 0.88 



Breadth 0.30 0.26 0.30 



Two cercariae, killed under cover-glass over flame, had the 

 following dimensions: 



Length 0.31 0.42 



Breadth, anterior 0.05 0.07 



middle 0.13 0.14 



posterior 0.06 0.06 



Anterior sucker 0.04 0.05 



Ventral sucker 0.07 0.06 



July 20, 120 snails from North Falmouth. A dozen or more 

 of these were dissected under a lens in the endeavor to find ex- 

 actly where the sporocysts occur but without finding any in 

 place. All the snails were then picked to pieces, washed, and the 



