882 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



sexual attributes. Secondary sexual characters comprise those attributes that 

 are not directly connected with the sexual organs, but that, nevertheless, con- 

 stitute marked differences between the sexes ; such are the greater size and 

 strength of man's body as compared with woman's, the superior grace and 

 delicacy of woman's movements, the deeper, rougher voice of man, and the 

 higher, softer voice of woman. In reality, all secondary sexual characters are 

 accessory to the primary ones, and the greater portion of the present article 

 will be devoted to a discussion of the latter. The primary sexual characters 

 of the male centre in the production of spermatozoa and the process of impreg- 

 nation, those of the female in the production of ova and the care of the devel- 

 oping embryo. 



Sexual Organs. Sexual organs are classified into essential and accessory 

 organs. The essential organs are the two testes of the male and the two 

 ovaries of the female. The accessory organs of the male comprise the vasa 

 deferentia, the seminal vesicles, the urethra, the penis, the prostate gland, Cow- 

 per's glands, and the scrotum and its attached parts. The accessory organs of 

 the female comprise the oviducts or Fallopian tubes, the uterus, the vagina, the 

 various external parts included in the vulva, and i\\e mammary glands. During 

 the greater part of life the sexual organs perform but a portion of their duties ; 

 only at intervals, and in some individuals never, do they complete the cycle 

 of their functions by engaging in the reproductive process itself. In the fol- 

 lowing account we shall discuss first the habitual physiology of the organs of 

 the male and of the female, and later their special activities in the repro- 

 ductive process. 



B. THE MALE REPRODUCTIVE ORGANS. 



The male reproductive organs, already mentioned, have as their specific 

 functions the production of the essential male germ-cells, the spermatozoa, the 

 production of a fluid medium in which the spermatozoa can live and undergo 

 transportation, the temporary storing of this seminal fluid, and its ultimate 

 transference to the outside world or to the reproductive passages of the female. 



The Spermatozoon. Spermatozoa were first discovered by Hamm, a 

 student at Leyden, in 1677. Hamm's teacher, Leeuwenhoek, first studied 

 them carefully. They were long believed to be parasites, even until near the 

 middle of the present century, when their origin and fertilizing function were 

 established. Spermatozoa are cells modified for locomotion and entrance into 

 the ovum. Human spermatozoa are slender, delicate cells, averaging 0.055 

 millimeter (^^ of an inch) in thickness, and consisting of a head, a middle- 

 piece, and a tail (Fig. 305). The head (A) is flattened, egg-shaped, with a thin 

 anterior edge and often slightly depressed sides. It terminates anteriorly in a 

 slender projecting and sharply pointed thread or spear. Its chief component 

 appears to be chrqnatic substance, and it is to be regarded probably as a 

 nucleus covered by an excessively thin layer of cytoplasm, von Bardeleben * 



1 K. v. Bardeleben : Verhandlungen der Anatomiscfien Gesellschaft ; Anatomischer Anzeiger, 

 vii., 1892. 



