14 Vetermary Obstetrics 



as 32 or 33 days, those of the female containing primitive ova, 

 while in the male there appear the tortuous cords, which are to 

 become the tubuli semeniferi and, in these columns are found 

 primitive sperm cells. Nagel doubts if there is any truly indif- 

 ferent stage in the development of the sexual organs, but be- 

 lieves that they can be distinguished at a very early date and that 

 probably they are at no time exactly alike. 



The primitive ova pass inwards toward the center of the gland 

 and, as they do so, undergo a progressive development, at first 

 having granular nuclei of indistinct outline, which soon enlarge, 

 becoming very distinct and of a regular spherical form, having a 

 double-contoured wall, fluid contents and a nuclear reticulum with 

 one or several nucleolar enlargements at the nodes. The whole 

 egg also increases greatly in size, its protoplasm becomes granular 

 and, between the ovum and the follicle or capsule, there is formed 

 an elastic investing homogeneous layer known as the zona radiata. 

 Having undergone this development, they are known as per- 

 manent ova. 



The smaller germinal cells arrange themselves in enveloping 

 layers about the permanent ova in the form of a hollow sphere, 

 from the walls of which, usually near the bottom, a discoid 

 eminence of small granular cells, the discus proligerus, appears 

 and, resting in this, is the ovum, while, \>&X^Nts.-Q.\h& discus prolig- 

 erus and the follicular wall, is the follicular liquid. Outside the 

 cellular wall the follicle is furnished with a fibrous, investing tu- 

 nic from the stroma of the gland and, when contiguous to the sur- 

 face, has, in addition, a covering of ordinary peritoneum. To- 

 gether these structures constitute Graafian follicles or ovisacs. 



Of all animal cells, the duration of life of the permanent ova is 

 best known. Unless they mature and are discharged into the 

 oviducts upon the rupture of the Graafian follicles, they remain 

 permanent from the date of birth, or soon thereafter, until the re- 

 productive powers of the animal have ceased as a consequence of 

 age. They remain in an unchanged state in the mare, for 

 example, for 20 to 25 years, capable at ahy time during that 

 period of becoming discharged into the oviducts, and, when im- 

 pregnated, of developing into a fetus. In all our domestic ani- 

 mals, so far as known, all permanent ova are developed at, or 

 very soon after, birth and hence, whenever such of these as are 



