ECOLOGY AND BIOLOGY OF THE PACIFIC WALRUS 



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The preserved ovaries were serially sectioned in 2- to 3-mm-thick slices and 

 were examined visually, without magnification. For interpretation of their 

 structural features, I referred mainly to Maximov and Bloom (1948), Ham 

 (1950), Cole and Cupps (1959), Enders (1963), Craig (1964), and Harrison and 

 Weir (1977). 



Definitions 



As the terminology that I use in the following account was drawn from several 

 sources and may not be universally understood, some definitions and indications 

 of the limits of my interpretations are necessary. 



Spermatogenesis is the entire process of development of the primary male germ 

 cells, beginning with the "dormant" spermatogonia and ending with the release 

 of free spermatozoa into the lumina of the seminiferous tubules. In the following 

 description of testis development, I have used this term also as the name for the 

 entire period in which the process takes place. That period is divisible into two 

 parts, recrudescence and spermiogenesis. 



Recrudescence is the prolonged, initial part of spermatogenesis, when the 

 spermatogonia undergo premeiotic divisions and eventually are transformed, 

 meiotically, into spermatocytes. It ends with the maturation division of 

 secondary spermatocytes to form spermatids. 



Spermiogenesis is the final part of spermatogenesis, beginning with the first 

 appearance of spermatids and ending with the last release of spermatozoa; it is 

 followed by retrogression of the seminiferous epithelium. 



Retrogression begins when the ranks of secondary germ cells degenerate and 

 pass into the lumina of the tubules. At its conclusion, only the spermatogonia and 

 Sertoli cells remain. This is a period of quiescence, followed by recrudescence. 



In the description of developments in the seminiferous epithelium, I have 

 reported only the two general types of spermatogonia: type A with a nucleus 

 containing diffuse, small, chromatin granules and a prominent, round nucleolus; 

 and type B with a large round to oval, darkly stained nucleus. Where 

 spermatocytes were present, both primary and secondary types were recognized. 

 Spermatids were so called from their first appearance at the end of the 

 maturation division of secondary spermatocytes until the time of their reduction 

 in size to spindle-shaped, deeply staining spermatozoa. 



For describing sexual development in relation to age, males were regarded as 

 potent when their testes contained spermatozoa or maturing spermatids (i.e., 

 when they seemed potentially capable of producing mature gametes). Fertile 

 males were those that had spermatozoa in the body of the epididymis, as well, 

 and probably had attained the capacity to fertilize ova. In the male, puberty is 

 the earliest appearance of potency; adolescence is the period from puberty to the 

 onset of fertility. The stibadult male is fertile, but his overall physical develop- 

 ment is not yet complete; the adult male has attained full physical and 

 reproductive maturity. 



In the female, pregnancy is the period beginning with fertilization of the ovum 

 and ending with birth of the calf. Gestation is the latter part of that period, from 

 implantation (nidation) of the blastocyst until birth. 



In the ovaries, all of the follicles that I detected visually were in their "second 



