TREMATODE SPOROCYSTS AND CERCARI^. 209 



2.5 millimeters in diameter. One of these cysts when crushed 

 proved to be filled with small granular cells irregular in outline. 

 Besides these, 3 small pearls were found in the mantle. There 

 were a number of small white cysts embedded in the mantle of 

 the other mussel. These contained pearls, 58 small pearls hav- 

 ing been obtained from them. Some of them were multiple. 

 They measured from 0.3 to 1.12 millimeters in diameter. 



On August 1 1 some small cyst-like yellowish masses of similar 

 appearance to those collected on the 24th, were found on the foot 

 and mantle of a mussel. Their contents resembled leucocytes. 

 A smear preparation revealed round cells of different sizes, the 

 prevailing size being about 0.0 1 millimeter in diameter, with very 

 strongly staining nuclei. A very careful examination of over 100 

 mussels made on different dates failed to yield any parasites. 



It is perhaps worthy of note that the redia stage is omitted 

 from the larval stages of trematode development which I have 

 found in the invertebrates of the Woods Hole region. 



Reference may here be made also to another abbreviated 

 trematode life history in the case of the distome, Parorchis avitus, 

 from the Herring GuU,^ where miracidia, still within the ova in 

 the later folds of the uterus, contained each a single well-de- 

 veloped redia. 



1 Proceedings of the U. S. National Museum, 46: 551-555- 



