18 THE NAUTILUS. 



SOME OBSERVATIONS ON THE GENITAL ORGANS OF UNIONID2E, 

 WITH REFERENCE TO CLASSIFICATION. 1 



BY DR. V. STERKI. 



The classification of the Unionidse is undergoing considerable 

 changes, owing to a closer study of their anatomy, and we are await- 

 ing Mr. Simpson's publication with considerable interest. In the 

 meantime a few observations made on many of our species, espe- 

 cially from the Ohio river drainage, may be worth communicating. 



1. The difference in the season of maturing ova and sperma, and 

 discharging the young, in the different groups, has been confirmed 

 by the examination of thousands of specimens from different waters. 

 In Lampsilis 2 , the ova and sperma are matured, and the former trans- 

 ferred to the branchiae, during summer. The young are mature in 

 fall, and a part of them discharged during October and November, 

 but most of them are retained until spring. Some of the branchial 

 sacks, single, or in groups of several, were found empty before win- 

 ter, e. g. in L. alatus and subovatus, and the same was found early 

 in spring ; but in most species, the marsupium was still fully charged 

 at that time. Very probably the time of spawning, as it has been 

 called, depends, to a certain degree, on the weather and the temper- 

 ature of the water. It would be of value to make such observations 

 in the south, and also on the Great Lakes. 



Quite different it is with the other Uniones, with a few exceptions. 

 Their branchiae are invariably found empty during fall, winter and 

 early spring, while the ovaries are charged with ova and the testes 

 with mature sperma. Their season of charging the branchiae, bring- 

 ing the young to maturity and dismissing them, is in the summer, 

 and naturally lasts a considerably shorter time than in Lampsilis 

 and the other winter breeders. 



This discrepancy in the season of propagating, in connection with 

 the different types of the uterus sacks, and the characters of the 

 shell, I consider very significant and pointing at a different phylo- 

 genetic origin of the several groups. They probably originated at 

 different geological ages and under different climatic conditions. 



In many species, the ovaries and testes were seen beginning 

 renewed activity while the young were still in the branchiae, and 

 this is probably so in general. 



the articles of Mr. C. T. Simpson in Am. Naturalist, April, 1895 and 

 the NAUTILUS XI, p. 19, and by the writer, the NAUTILUS IX, p 91. 

 3 A well characterized and well defined genus. 



