11 



their greater relative developmeut iu the fetus is indicative of a 

 future male development. In very young embryos, the growth is 

 very rapid, followed, however, by a period of atrophy, during 

 which the seminiferous tubules undergo marked development. 

 Pende (21) states: " There seems to be an inverse relation be- 

 tween the growth of the tubular and interstitial tissues, as one is 

 hypoplastic when the other is in full activity." From birth to the 

 onset of sexual maturity, whicli may be called a period of rest for 

 the testicle, the cells are few in number. With the accentuation of 

 the secondary sexual characters, and the beginning of sexual life, 

 these cells again increase in number and acti^-ity. 



The parenchyma of the testis consists for the most part of the 

 seminiferous tubules, which, on account of the courses they take 

 in the different regions, are divided into groups. The peripheral 

 tubules are the much-contorted tubuli contorti. These anastomose 

 to form the mucli shorter tul)idi recti. These in turn anastomose 

 frequently, uniting to form the rete testis. The rete proceeds 

 through the mediastinum to form the efferent ductules which 

 break through the tunica albuginea to form the greater part of the 

 liead of the epididymis. The tubuli contorti are the longer and 

 more numerous of the tubules, for it is liere that practically all 

 the spermatozoa are produced. The straight tubules are relatively 

 so short that they may be regarded more in the light of the begin- 

 ning of the system of excretory ducts. 



The seminiferous tubules consist of a thin peripheral meml)rana 

 l)ropria upon which rests tlie seminal e])ithelium, which is made up 

 of the essential semen forming cells, and the cells of Sertoli. The 

 spermatogenic cells may be divided into three groups, from within 

 outward: the peri])heral single layer of small cuboidal spermato- 

 gonia ; one or two rows of large spermatocytes ; and three to five roAvs 

 of spheroidal spermatids. Tlie cells of Sertoli are more or less of the 

 syncitial type. — large in size and irregular in outline. They occur 

 at various intervals between the layers of spermatogenic cells, with 

 their bases resting upon the mcmbrana proi)ria. Centrally they 

 send out protoplasmic processes for variable distances,— some 

 even reaching the l)order of the innermost cell layers. 



Spermatogenesis: In this process, the ])rimary germinal cells, 

 the spermatogonia, divide to form the i)riniary spermatocytes, 

 ^laturation consists of two cell divisions of tlie primary sperma- 

 tocytes, and these in turn form four spermatids. During the pro- 

 cess, the number of chromosomes is reduced to half the number 

 characteristic of the species. The spermatids then become con- 

 verted into mature spermatozoa. Tliis mode of transformation 

 may be seen in Plate I. In the process, the nucleus of the sperma- 

 tid forms a large part of the head; the eentrosome divides, part 

 passing to the extremities of the neck. One eentrosome ])ecoraes 

 the .interior, and remains altaelied to the head, while tlie other 

 divides to form the posterior eentrosome. The latter is divided 

 into the anterior part, and the posterior nodule or annular ring. 



