188 OVARY AND PAROVARIUM, BY W. WALDEYER. 



are both obviously subservient to the development of ova, it is 

 certain that the germinal vesicle and germinal spot are formed 

 by the germ-stock ; but in addition, as Bischoff has observed, a 

 quantity, though often small, of finely granular protoplasm 

 lies around and between the germinal vesicles even at the 

 extremity of the germ-stock, and the nearer the ova approxi- 

 mate the excretory duct of the germ-stock, the more distinctly 

 visible is the protoplasmic area surrounding each germinal 

 vesicle, and each ovum comes to present the appearance of a 

 complete cell, composed of protoplasm (or yolk), a nucleus, and 

 a nucleolus ; the ova, therefore, of the germ -stock are com- 

 parable with the primordial ova of Vertebrata. It is generally 

 stated that in the germ-stock the germinal vesicles are alone 

 developed, and that the whole of the protoplasm constituting 

 the vitellus proceeds from the yolk-stock. I cannot, however, 

 coincide with this view, and hold, with Gegenbaur (45, p. 287), 

 that a fine investment of protoplasm surrounds each ovum as 

 it leaves the germinal area. Moreover the morphological 

 significance of the yolk-stocks is by no means certainly 

 established. Gegenbaur (45) expresses the opinion that they 

 are " parts of an extensive ovarium, of which only the smallest 

 portion remains persistent, the greatest portion, on the other 

 hand, degenerating to form the yolk-stocks." However this may 

 be, it is certain that ripe completely formed cells, comparable 

 to the primordial ova of the Vertebrata, originate in the germ- 

 stock, or true ovarium. The researches of Stieda (135), G. 

 Walter (124), and Leuckart (67), which I am able to corrobo- 

 rate from observations made on the Ascaris nigrovenosa, show 

 that the ova themselves proceed from the epithelial cells of the 

 ovarian tube. At any rate the most various transitional forms 

 may be found, and at the distal extremity of the ovary the 

 youngest ova and epithelial cells can no longer be distinguished 

 from each other. And so we find in the Ascaridae, that as the 

 ova press forward in the genital tube the granular yolk-mass 

 surrounding each germinal vesicle augments in quantity, and 

 at a later period acquires a thicker or thinner vitelline mem- 

 brane. The increase in the granular yolk, as is shown both by 

 Leuckart's (67) observations and my own, is attributable to 

 the epithelium investing this part of the genital tube. 1 must 



