346 ANNUAL OF SCIENTIFIC DISCOVERY. 



and cornutus were common in the canal near Cleveland. At this 

 time a living specimen can hardly be found. 



During the present season we have seen workmen excavating por- 

 tions of mud, that contain great numbers of dead shells of these and 

 other scarce species. Perhaps, in another age, similar operations may 

 expose to view similar remains, which may puzzle the geologist to tell 

 at what period they existed. 



ON THE SEXES AND HABITS OF SOME OF THE ACEPHALOUS BIVALVE 



MOLLUSCA. 



THE following is an abstract of a communication presented at the 

 meeting of the American Association, Cincinnati, by Dr. J. P. 

 Kirtland : 



The fluviatile bivalves of North America are principally embraced by 

 the genera Unio, Anodonta, and Alasmodonta, and are appropriately 

 arranged in the Larnarkian family of Naiades. In the waters of the 

 State of Ohio are found sixty-four or five species ; perhaps a larger 

 number. Most naturalists and anatomists have considered them as 

 hermaphrodites, though some discrepancy of opinion has been enter- 

 tained. A familiarity with their habits, and a series of dissections, 

 long since convinced ine that the commonly received opinion was 

 incorrect. 



This conclusion was founded upon the facts, that very many species 

 present, in their shells, two varieties of forms, in about equal numbers, 

 and that, with one form, is associated animals Avith oviducts, which, 

 at certain seasons, teem with young, while the inhabitants of the other 

 form remain permanently barren. Subsequent investigations have 

 shown, that it is applicable to about two thirds of the American spe- 

 cies. In a few others, no difference in form is discernible between the 

 shells of the prolific and barren varieties. If minute dissections, aided 

 by the microscope, have discovered and demonstrated the existence of 

 both male and female organs in the same individuals, of course I must 

 abandon the position I have taken ; but if their hermaphrodite struc- 

 ture be a mere matter of inference, as I suspect it is, drawn from the 

 failure to discover any anatomical difference between the prolific and 

 barren individuals, then the probabilities are in favor of their being 

 dioecious. 



The several families of mollusca present examples of all modes of gen- 

 eration ; some are hermaphrodite, others are dioecious. Several pos- 

 sess the faculty of self-impregnation ; others, though hermaphrodite, 

 require a reciprocal coitus ; and the mode of fecundating, in those in 

 which the sexes arc distinct, is not, in all instances, understood. The 

 animals of the Cephalopoda are distinct, the male and female organs 

 being found in different individuals. The Pteropoda are all hermaphro- 

 dite, and their sexual organs are discoverable. In some of the Gaster- 

 opoda the sexes are separate, in others united. Though the fourth 

 class of Cuvicr's mollusci the Accphala have generally been con- 

 sidered as hermaphrodite, analogies are equally in favor of their being 

 dioecious ; or, like the third class, perhaps some species may be her- 



