18 THE NAUTILUS. 
SOME OBSERVATIONS ON THE GENITAL ORGANS OF UNIONIDE, 
WITH REFERENCE TO CLASSIFICATION.! 
BY DR. V. STERKI. 
The classification of the Unionide 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’, the ova and sperma are matured, and the former trans- 
ferred to the branchiz, 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 branchiz 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 branchiz, 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 branchix, and 
this is probably so in general. 
1 See the articles of Mr. C. T. Simpson in Am. Naturalist, April, 1895 and 
the NauTiLus XI, p. 19, and by the writer, the Nautitus IX, p 91. 
? A well characterized and well defined genus. 
