318 DR. MARTIN BARRY'S RESEARCHES IN EMBRYOLOGY. 



56. Bernhardt, as already said, by rupturing this membrane demonstrated its real 

 nature. In cases, too, where he viewed the " ovulum" (ovum) freed from its sur- 

 rounding granules, he appears to have regarded it, in its whole thickness, as the 

 " membrana externa ovuli-f-;" but in those instances in which granules were ad- 

 herent to the ovum, concealing the outer surface of this thick membrane, the sub- 

 stance of the latter was mistaken by Bernhardt for a " zona pellucida," or " spatium 

 pellucidum ;" and the part which this author indicates as the " membrana ovuli ex- 

 terna," is obviously the internal surface of the chorion. See Plate VIII. fig. 72. J, 

 and the description of the Plates. 



Parasitic Ovisacs. 



b7. Minute ovisacs Qi) are seen in Plate VIII. fig. 75, in the parietes of a Graafian 

 vesicle {h i) of one of the Mammalia, the Dog. The same Plate, fig. 76, presents a num- 

 ber of ovisacs similarly situated in the corresponding structure of a bird, the Pigeon §. 

 If such a Graafian vesicle or corresponding structure be crushed, the ovum contained 

 in its cavity escapes, but the minute ovisacs in its parietes remain unmoved. I have 

 counted more than fifty of the latter, scarcely exceeding their primitive size, in the 

 parietes of one of these structures from the Bird, none of which probably would have 

 been matured. Sometimes these minute ovisacs appear to have originated in the 

 substance of the covering acquired by a larger ovisac ; and sometimes they seem to 

 be included by the covering which the larger ovisac acquires. An instance of the 

 latter is seen in Plate VI. fig. 36, where two small ovisacs are so included ||. The 

 minute ovisacs in such a situation, whether originating there or contained in it by in- 

 clusion, I propose to call parasitic ovisacs. 



58. Plate VIII. fig. 77' presents one of these parasitic ovisacs^ {h) contained in the 

 parietes of a Graafian vesicle of the Ox. Both have been divided, one half of each 

 remaining in the ovary, the other being reflected. At fig. 78. is an enlarged view of 

 the two halves of the divided parasitic ovisac^ seen in fig. 77- The proper mem- 

 brane {h) is seen lined by the membrana granulosa (^) ; and within the latter is a 

 dark space, the cavity of the parasitic ovisac which contains the oVum (/). Fig. 79. 

 presents a transverse section of this parasitic ovisac ; h being its proper membrane, 

 and g granules of the membrana granulosa. The proper membrane {h) of the para- 

 sitic ovisac in this instance measured V" in thickness, and its cavity distended under 

 the compressor 1^'" in length. 



t Symbolse, &c., figs. ii. iii. iv. x. &c. 



X Fig. xxiii. of Bernhardt. This is the figure before referred to in the description of the proper membrane 

 of the yelk (50. Note). 



§ I have seen minute ovisacs similarly situated in a Chelonian reptile. 



II In this instance the included ovisacs are contained in the incv^xQxA pedicle already mentioned (44). 



% Incipient Graafian vesicle ? 



