620 



MAMMALIAN EMBRYOLOGY 



Second, parturition, or the actual time of birth. The condition of 

 the offspring at the time of parturition varies to a considerable extent. 

 Some animals are born with the ability to walk and take reasonable 

 care of themselves within a very short time after birth, while some are 

 quite dependent upon their mother for a long time. 



Third, the period of adolescence, which is that period of life in the 

 young devoted entirely to growth and development. It extends from 

 birth to sexual maturity. 



Fourth, adult life, or the period of sexual maturity. During this 

 period many physiological changes often take place in the individual 

 entirely aside from those of the reproductive system. 



FERTILIZATION 



As the egg is thrown out of the Graafian follicle (Fig. 355), it passes 

 into the oviduct (Fallopian tube) and is carried by the cilia in the oviduct 

 to the uterus. If fertilization takes place, the sperm, which finds its way 



A 



C. 



Fig. 355. 



A. Section of well-developed Graafian follicle from human embryo (von Herff) ; the 

 enclosed ovum contains two nuclei. B. Ovary with mature Graafian follicle about 

 ready to burst (Ribemont-Dessaignes). C. Section of human ovary, showing 

 mature Graafian follicle ready to rupture. Kollmann's Atlas. 



