182 OVARY AND PAROVARIUM, BY W. WALDEYER. 



the centre of which it forms an enlargement, of the size of a 

 pea, the Latebra or yolk cavity of Purkyne' .* 



The principal yolk with its germinal vesicle, independently 

 of its size and the early disappearance of the germinal spots, 

 presents no special peculiarities ; it represents the primordial 

 ovum. The chief difficulty in regard to the egg of the Bird 

 lies in the question of the origin of the food yolk, and its rela- 

 tion to the primordial cell of the ovum. 



In regard to the historical aspect of this matter it may here be 

 briefly remarked that since the discovery of the mammalian ovum by 

 v. Baer, two opposite views have been held in regard to the egg of 

 the Bird; of tbese, one, supported by Schwann (104), Gegenbaur 

 (43), Leuckart, Kolliker (58), Cramer (34), regards the whole egg of 

 the Bird as a single cell; whilst the other, held by H. Meckel (73), 

 Allen Thompson (115), Ecker (37), Strieker (114), His (53), and 

 others, considers both the food yolk and the vitelline membrane to be 

 secondary formations, and, in fact, as products of the follicular epi- 

 thelium. Another controversy again has arisen in reference to the 

 nature of the elements of the food yolk. Schwann (104) and Klebs 

 (56), and more recently His (53), contending that they are cells, 

 whilst others, especially Gegenbaur (43) and Strieker (114), hold 

 them to be spheroidal bodies of peculiar nature, which have no claim 

 to the dignity of a cell, but may rather be associated with such 

 colloidal drops or albuminoid particles as are found in secretions. 



The egg of the Bird, in its earliest state, is exactly like that of 

 the Mammal (see fig. 193, B c D), except that the follicular epi- 

 thelium always remains as a single layer, which I may mention 

 in opposition to the statement of His (53). An increase in the 

 contents of the follicles may soon be observed; a fluid analogous 

 to the liquor folliculi is, however, never produced, but a finely 

 granular mass that is deposited around the principal yolk, from 

 which it can be clearly distinguished. This is the first rudi- 

 ment of the secondary yolk mass ; the principal yolk in the 

 meanwhile remains essentially unaltered. As the follicle ad- 

 vances in age, the small granules of the secondary yolk aug- 



* The term "cavity" refers to the fact that in the boiled egg this 

 spherical white mass of the yolk does not usually coagulate, but remains 

 fluid, which gave rise to the idea that there was a cavity filled with fluid. 



