THE NAUTILUS. 31 



One specimen of U. rubiyiitosus Lea, (Ohio Canal, May) had a 

 few acini producing ova in the gonad charged with copious sperraa. 

 In that instance the distinction was easy, for the bright crimson 

 color of the ova. Among 120 specimens of U. pt/ramidatus, from 

 the Ohio River, collected late in September, two were found contain- 

 ing ova and sperma in the same gonads. Of U. parviis Barnes one 

 specimen had a good quantity of sperma beside ova in abundance. 

 This case especially needs revision. Among a limited num-ber 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. Or a large num- 

 ber of specimens might be marked in some way, in a pond or certain 

 place of a 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 branchire, 

 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 ayamogenesis and parthenogenesis, in 

 Unionidce, 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 froai 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 



