McCrady.] 172 [Dec. 3, 



Reproductive Organs. 



Though my attention was directed specially to the subject of the 

 fertilization of the ova in the oyster, I was never able to procure any 

 light on the subject. Davaine was similarly unsuccessful in 0. edulis. 

 His determination, however, that the oyster is hermaphrodite was 

 fully borne out by my observations ; which all tended to show that 

 the male organ consists in every part of a solid branching stem, con- 

 sisting wholly, as far as I could ascertain, of spermatocysts ; and that 

 this stem was everywhere completely surrounded and enclosed by 

 the ovary, consisting usually of a granular common yolk-mass, in 

 which are scattered at intervals everywhere germinative vesicles of 

 various sizes, and with no enclosing membrane, so that they may be 

 broken up by pressure into fragments which immediately each assume 

 the spheroidal form, and then appear only as germinative vesicles of 

 a smaller size. * The spermatozoa are developed, or begin to be de- 

 veloped, and assume their perfect free form often long before the ova 

 would be considered, according to the analogy of other animals, as 

 ready for impregnation, that is, while they are still only scattered 

 germinative vesicles everywhere enclosed in a common yolk mass. 

 The spermatozoa may be seen in their aggregated, or even their free 

 condition, actively moving about among masses of this granular yolk- 

 substance enclosing many germinative vesicles, without exhibiting 

 any attraction for them, and without the appearance of any change 

 in the young vesicles themselves. The spermatozoa have, as de- 

 scribed by Dr. Burnett, an ovo-globrdar head and a delicate tail, 

 which I did not succeed in tracing but once to its extremity, and 

 which always seemed to me rather short. 



The ova were observed by Davaine in a subsequent condition, in 

 which they were no longer simple germinative vesicles embedded in a 

 common yolk mass, but a condition in which each such simple vesi- 

 cle appears to be surrounded by a separate yolk of its own. But he 

 was unable to ascertain whether or not the egg of the oyster ever 

 presents the ordinary form among animals, viz., a vitelline membrane 

 enclosing a yolk, within which are found a germinative vesicle, con- 

 taining a nucleus, or nucleus and nucleolus. Nor did he succeed in 

 discovering whether, as in other Acephala, the ova ever became en- 

 closed each in a separate and usually pyriform sac of the ovarian 

 membrane. 



I was fortunate in having the opportunity to observe the ova in 



