PHYSIOLOGY, CHEMISTRY AKD PATHOLOGY 449 



IV. Functions of the Internal Secretion of the Testes 



1. Influence of the Testicular Hormone upon the Development of 

 the Generative Organs. A consideration of the embryology and subse- 

 quent development of the generative organs shows that the interstitial 

 cells affect their development, For convenience the developmental rela- 

 tionship existing between the somatoplasm and germplasm may be consid- 

 ered under the following headings : Primary and Secondary Undifferen- 

 tiated Stages, and Primary and Secondary Differentiated Stages (Whee- 

 lon). 



Undifferentiated Stages. In the higher forms of life the presence of 

 the. germplasm manifests itself only after marked development of the 

 somatoplasm. In human embryos up to a length of 14 mm. sex cells, 

 though developing, are not recognizable histologically. Hence, this period 

 may be called the Primary Undifferentiated Stage of sexual development. 



The Secondary Undifferentiated Stage is illustrated in embryos from 

 14 to 24 mm. in length, in which aggregates of cells are recognizable as 

 testes or ovaries. At this time the Wolffian and Miillerian ducts, which 

 later give rise to either male or female internal secondary sex organs, are 

 being laid down. Such embryos, although possessing well established re- 

 productive cells, are sexually neutral or somatically indifferent, hence 

 the primordia of the genital glands are independent of the generative 

 organs. 



Differentiated Stages. Immediately following the secondary Undiffer- 

 entiated stage, vascularization of the sex glands occurs and the embryo 

 enters upon the Primary Differentiated Stage. This period, beginning in 

 the 24 mm. embryo, is continued to puberty. The Miillerian and Wolffian 

 ducts undergo marked alterations; either the Wolffian ducts continue de- 

 velopment and form the excretory ducts of the testes, or the Miilleran ducts 

 partially fuse to form the uterus and tubes. When the further develop- 

 ment of either of these pairs of ducts is determined the development of the 

 other pair ceases and soon retrogressive changes ensue. Because of these 

 somatic alterations the sexually Undifferentiated character of the embryo 

 is lost. 



Vascularization of the gonads and sex differentiation are intimately 

 associated, hence it may be assumed that a principe is liberated from the 

 germ cells or from tissues closely associated with them at the reception of a 

 blood supply which acts in such a manner as to bring about sex differentia- 

 tion. Sex organs are not present until differentiation has taken place and 

 the embryo has assumed male or female characteristics, hence sex cannot 

 be ascribed to the embryo until genital organs appear, even though repro- 

 ductive tissue of one sex is present. Granting that the sex of the ovum is 

 determined at the time of fertilization, sex, as such, does not appear until 



