346 MONOECIOUS MOLLUSCA. 



of innumerable ova forming a granular fluid, at the very 

 time when the male was turgid with a white milk of the con- 

 sistence of honey. * Baster not only believed in the bi- 

 sexual nature of the oyster but of the mussel also, which, 

 he tells us, is big with ova in April and May. At this time 

 he observed some of them to eject a milky fluid diffusible in 

 water, and hence he presumed they were masculine ; others, 

 at a later period in May, were noticed to eject at short inter- 

 vals, during the space of nearly two hours, oblong bodies 

 not unlike the excrements of mice, which fell in a little heap 

 within a short distance of their parent. After about six 

 hours these bodies had become flat like a plate ; next day 

 they separated readily by a slight agitation of the water, 

 and a few being placed under the microscope, it was seen 

 that they were evidently the young of the mussel. The 

 observations of M. Prevost, of Geneva, published in 1825, 

 do not appear to be more conclusive than those of Baster. 

 They relate to the Mya pictorum. " If, towards the spring," 

 says M. Prevost, " we examine the organs of generation in 

 some individuals of this species, we are struck at the first 

 glance with the different products which they emit. While 

 we find in some individuals a true ovary, and ova in abun- 

 dance, in others the analogous organs, and similarly placed, 

 contain nothing but a thick liquid of a milky colour, which 

 under the microscope appears to be crowded with animal- 

 cules in motion. These marked differences are neither the 

 result of chance, nor of a subsequent change in the condition 

 of the ovary. The Myas in which ova are found present no 

 trace of the thick and milky fluid ; and, on the contrary, 

 those which possess this liquid produce no ova." From 

 somewhat similar observations I find it stated that the genera 

 Anomia, Teredo, Dreisseina, Venus, and Cardium, are also 

 separately masculine and feminine ; but surely Wagner has 

 travelled fast to a generalization if it is from such limited 

 data that he has concluded the class of bivalves to be, with 

 very few exceptions, animals of distinct and separate sexes. -j- 

 Mr. Garner, no mean authority, has come to an opposite 

 conclusion, apparently questioning the accuracy of the ob- 

 servations which would seem to prove that even the genera 

 quoted are bisexual. " There appears," says Mr. Garner, 

 " every reason to believe that there is no difference in the 

 individuals as to sex, and that the ova are discharged from 

 the ovaries in a state fit to develope, without the necessity 



* Exercit. Anat. tert. p. 9. 



t Miiller's Elem. of Physiology, trans. 857. Professor Owen has come 

 to the same conclusion as Wagner. Lect. Invert. Anim. 287. 



