94 EDGAR ALLEX. 



this theory. But if the natural course of evolution of reproduc- 

 tion be followed, parasitism must be considered a secondary 

 development. It is possible therefore that metamorphosis with- 

 out parasitism is the primitive method and that Anodonta 

 imbecillis never has relied upon parasitism for development. It is 

 also possible that the shorter reproductive cycle is the primitive 

 one rather than an adaptation from one similar to that of other 

 species of Unionidae. 



SUMMARY. 



Anodonta imbecillis cannot be classed with either long or short 

 term breeders as defined by Lefevre and Curtis. In specimens 

 obtained at Fairport, Iowa, a complete reproductive cycle (in- 

 cluding metamorphosis from glochidia to juvenile mussels, for 

 reproduction in this species does not depend on parasitism) is 

 completed in from 3 to 4 weeks during the late summer. Another 

 cycle begins after an interval varying from 2 to 3 days to 2 \veeks. 

 Gravid A. imbecillis have been found in all months but April. 

 It is possible therefore that this short reproductive cycle is re- 

 peated throughout the year. 



LITERATURE CITED. 



Coker, R. E., Shira, A. F., Clark, H. W., Howard, A. D. 



'i9-'2O Natural History and Propagation of Fresh Water Mussels. Bui. 



Bureau Fisheries, Vol. 37, No. 893. 

 Howard, A. D. 



'15 Some Exceptional Cases of Breeding among the Unionidea. Nautilus, 



Vol. 29, p. 4-11. 

 Howard, A. D., and Anson, B. J. 



'22 Phases in the Parasitism of the Unionidae. Jour. Parasitology, Vol. 22, 



p. 68. 

 Lefevre, G. and Curtis, W. C. 



'12 Studies on the Reproduction and Artificial Propagation of Fresh Water 



Mussels. Bui. Bureau Fisheries, Vol. 30. 

 Lillie, F. R. 



'95 The Embryology of the Unionida-. Jour. Morph., Vol. 10, p. i-ioo. 



