THE NAUTILUS. 31 
One specimen of U. rubiginosus Lea, (Ohio Canal, May) hada 
few acini producing ova in the gonad charged with copious sperma. 
In that instance the distinction was easy, for the bright crimson 
color of the ova. Among 120 specimens of U. pyramidatus, from 
the Ohio River, collected late in September, two were found contain- 
ing ova and sperma in the same gonads. Of U. parvus Barnes one 
specimen had a good quantity of sperma beside ova in abundance. 
This case especially needs revision. Among a limited number of 
Anod. imbecillis four specimens (Ohio Canal, May) were found with 
ova and sperma in various proportions. 
The question whether such individuals are capable of self-im- 
pregnation, might be decided by experiment on such species where 
hermaphroditism is frequent. 
It has also been said that a total change of the sexes may take 
place in an individual, and that question also could be settled only 
by long continued observation and experiments. Ora large num- 
ber of specimens might be marked in some way, in a pond or certain 
place ofa river or creek, and as many as can be found again, would 
be controlled year after year. That, however, would be necessary 
only for such forms in which the shells show no sexual differences. 
While such a change is a priori improbable in all Uniones, it ap- 
pears really absurd in regard to those forms in which the sexes are 
established and manifested by permanent characters of the branchiz, 
and also the shells, as in Lampsilis and some others. 
It may be mentioned here that, as to my knowledge, observations 
on the question of possible agamogenesis and parthenogenesis, in 
Unionide, have not been made. Carefully conducted experiments 
might give interesting results in that direction. They would neces- 
sarily be difficult, for the possibility of hermaphroditism and self- 
impregnation, in every instance. 
5. Sexual differences of the shells—In Lampsilis, as well known, 
the posterior inferior part in the female mussel is dilated to make 
room for the marsupium, yet this dilatation is very various in kind 
and degree. But the differences sometimes are in a certain measure 
relative, owing to the nature of the habitat, and to inheritance. L. 
luteolus, e. g., in certain localities, is so short and inflated that the 
males may closely resemble the females from other places where the 
mussels are more slender. 
In most other “ Uniones,” the differences are little marked. Yet, 
in general, the females are more inflated than the males, as in 
