74 



to all vertebrated animals, but hitherto regarded as the inner mem- 

 brane of the " foUiculus Graafianus " in Mammalia, and by some 

 authors denominated the " chorion " in other Vertebrata. He also 

 describes the real nature of the " foUiculus Graafianus," and its re- 

 lation to the calyx of the Bird ; the germinal vesicle and its con- 

 tents, as being the most primitive portion of the ovum ; the order of 

 formation of the several other parts of the ovarian ovum ; and the 

 true chorion of Mammalia as being a structure superadded within 

 the ovary. 



In the second part the author describes a granulous tunic of the 

 ovum of Mammalia not hitherto observed ; the manner of origin 

 of the " membrana granulosa " of authors ; the different situations of 

 the ovum in the Graafian vesicle at certain periods ante coitum, not 

 hitherto observed ; and certain structures by means of w^hich the 

 ovum is made to occupy these several situations. 



The follovi^ing are the principal facts made known by Dr. Barry 

 in this memoir ; but other facts are also mentioned, which he in- 

 tends to make the subject of a future communication. In Mammalia 

 and in Birds the germinal vesicle and its contents are those parts 

 of the ovum which are first formed. The germinal vesicle at an 

 early period is surrounded by peculiar granules, forming an envelope 

 not hitherto described. The ovum of all vertebrated animals is con- 

 tained in a vesicle (the " chorion " of some authors, found in Birds, 

 Amphibia, and Fishes), which is essentially the same in structure 

 wherever found, and which he thinks it desirable universally to 

 denominate an ovisac. This vesicle is the " couche interne" of 

 the Graafian vesicle, as described by Professor Baer. The Graafian 

 vesicle of Mammalia is nothing more than an ovisac that has 

 acquired a covering or tunic, susceptible of becoming highly 

 vascular, which covering is the " couche externe " of the Graafian 

 vesicle as described by Baer. The ovisac of Birds, Amphibia, and 

 Fishes ("chorion" of some authors), acquires in like manner a 

 covering or tunic, susceptible of becoming highly vascular ; and by 

 the union of the ovisac with this covering, there is constituted a 

 structure analogous to the Graafian vesicle of Mammalia. The quan- 

 tity of yelk in the former being large, that portion of the ovary 

 which contains the structure here referred to (as analogous to the 

 Graafian vesicle of Mammals) becomes pendent ; and now the united 

 coverings of the yelk-ball, — viz. the ovisac, its external tunic, the 

 ovarian stroma, and the peritoneal investment, — are together called 

 the calyx. From this it will be obvious that the Graafian vesicle is 

 not a structure peculiar to Mammalia, as it has been supposed. 



The ovisac has at first an elliptical or ellipsoidal form, becomes 

 more spherical, and in Mammalia is often met with somewhat tapered 

 at one end. The structure of the ovisac in some of the Mammalia 

 may be examined when it does not exceed in length the 50th or 

 even the 100th part of a Paris line, that is, in the latter case, the 

 1125th of an English inch. Myriads of ovisacs with their contents 

 are formed that never reach maturity. Some of the ovisacs which 

 do not reach maturity are situated in the parietes of Graafian 



