118 On the Sexual Characters of the Family of Naiades. 
mists have been decidedly of the opinion that the animals of this family 
are hermaphrodites, but Mr. Prevost of Geneva affirms, that he observ- 
ed in some individuals of the Unio pictorum, the existence of spermat- 
ic animalcule, which he could not perceive in those, which contained 
eggs. He therefore, inferred, that the sexes were distinct. ‘This 
led Blainville to a re-examination of the subject: he dissected about 
forty individuals of the genera Unio and Anodonta, without discov- 
ering any indications, that could lead him to suppose the existence 
of the male sex; still however he is in doubt, and we are much m- 
clined to believe, with Ferussac, that Prevost may be right ; but that 
more observations and more observers are required, fully to establish 
this disputed point, although Baer, has gone far towards even this 
subject. 
“Treviranus, also made some interesting observations, on this sub- 
ject, an account of which is published in the “ Zeitsch. fur Physiol.” 
in 1824. He was of the opinion, that the same organs produced 
both the ova and the fecundating fluid. He however remarks, that 
he found at the season of excluding their eggs, many that were en- 
tirely destitute of them.” 
Barnes, in the sixth Vol. of the Am. Journal of Science, p. 114, 
says that ‘ They are generally supposed to be hermaphrodites per 
se.” Profs Rafinesque 1 in his Monograph of the Fluviatile Bivalve 
Shells of the river Ohio, makes a concurrent statement. 
In the course of the three last years, I have dissected many oe 
dreds of them, and carefully observed their habits, under a variety 
of circumstances, until I am persuaded, that the sexes are distinct, 
and that each sex, possesses a peculiar organization of body, asso- 
ciated with a corresponding form of the shell, sufficiently well mark- 
ed, to distinguish it, from the other. 
The essential distinguishing mark of the females, discoverable in 
their internal structure, is the presence of ovaries, and oviducts, 
which may be seen, attached above to the branchiz, and resting be- 
low, on the posterior* basal margin, at a point represented by (a,) 
in the annexed diagram. ‘To enable these viscera, to perform their 
natural functions without interruption, this portion of the shell is in- 
variably somewhat produced, and ventricose, more in some species 
than in others; and the posterior margin is generally truncated, and 
* Posterior if we refer to the natural position of the animal. 
