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 animalculse, 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 in- 

 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. 5 ' 

 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" Prof. Rafinesque 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 hun- 

 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 branchiae, 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. 



