304 PHYSIOLOGY FOB DENTAL STUDENTS. 



that of conjugation in lower forms. In this process, cells of two 

 types are concerned, the male, or sperm cell, or spermat ozoon, 

 and the female cell or ovum. The spermatozoon has the ability 

 to move and to penetrate the ovum. The nuclear elements of 

 both cells unite to form a new nucleus, which is then capable of 

 undergoing a long series of subdivisions. In changes which piv- 

 cede fertilization, the nuclear material originally present in bolli 

 male and female cells is reduced, and when the cells fuse, the re- 

 sulting nucleus contains a normal quantity of nuclear material. 



The Accessory Phenomena of Reproduction in Man. 



The beginning of the active sexual life in man is between lin- 

 ages of fourteen and sixteen, and is called the age of puberty 

 In both boys and girls the whole body shows a marked develop- 

 ment at this time. The growth of hair on the pubic regions and 

 arm pits, and on the face of boys, the deepening of the male 

 voice, and the development of the breasts in the female, are all 

 accompanying phenomena of the development of puberty. In 

 females the age is marked by the onset of menstruation, which 

 consists of a periodic flow of mucus and blood from the uterus 

 The flow lasts from four to five days, and recurs with great reirii- 

 larity about every four weeks. In males fully formed seminal 

 fluid, containing live sperm cells, is secreted, and erections of the 

 penis occur. 



The Female Organs of Reproduction. These are the ovaries, 

 oviducts, uterus and the vagina. The ovaries are paired bodies 

 lying in the lower part of the abdominal cavity and held in posi- 

 tion by the broad ligament. The cells from which the ova de- 

 velop are imbedded in the fibrous tissue of the ovary. A number 

 of these cells, better developed than their fellows, and surrounded 

 by a layer of cells, which form a sort of follicle, lie near the sur- 

 face of the ovary. These are the Graafian follicles, in which the 

 ova develop till they are ripe, when they are extruded into the 

 abdominal cavity by rupture of the follicle. In very close appo- 

 sition to the ovaries is a tube, the oviduct, which leads to the 

 uterus. The outer end of this tube is fimbriated, and it is fur- 

 nished with cilia, the movements of which cause currents in the 



