Chap. 18 



REPRODUCTION 



347 



Eqq Nests 



Primary 

 Follicle 



Double- 

 layered 



Beqinninq 

 of Antrum 



Atretic 

 Follicle 



Follicle Approadiinc] 

 Maturity 



Atretic Follicle 



Mature 

 Follicle 



Corpus 

 Albicans 



.Ruptured 

 Follicle 



Fully Formed/ 

 G)rpu5 Luteum 



Connective 

 Tissue of Ovary 



Conn.Tissue 

 Lutein Cells 

 Fibrin of Clot 

 Coaoulated Blood 



4iW^' Released 



Younc]t 

 "Corpus 

 Luleum 



Fig. 18.11. Diagram of a cut tfirougli a mammalian ovary showing a sequence 

 of stages in the growth and maturity of the ovarian follicle, the egg and its sur- 

 rounding sac; the rupture of the sac and release of the egg; and the transformation 

 of the sac into a gland, the corpus luteum. At the left, the strands of the mesova- 

 rium attach the ovary to the body wall. Follow the sequence clockwise around the 

 ovary, starting at the mesovarium. Note the atretic follicle, one which abruptly 

 ceases to grow before maturity and then degenerates. In the human ovary only one 

 ovum ordinarily matures each four weeks during the active life of the ovary. (Cour- 

 tesy, Patten: Human Embryology, ed. 2. New York, The Blakiston Co., 1953.) 



mother's body, inevitably reaching the ovary. During the first half of preg- 

 nancy, the corpus luteum is affected by these substances and becomes about 

 the size of a grape. Under stimulation from them and the pituitary gland, the 

 corpus luteum conditions the uterus to hold the embryo until the time when 

 hormones secreted by its placenta take part in this function. 



The uterus is the organ within which the mammalian embryo is sheltered 

 and nourished. This period (gestation) may be short or long, three weeks in 

 a mouse, nine months in man, two years in elephants. An embryo enters the 

 uterus as a minute ball of cells and leaves it via the vagina or birth canal 

 as a well-formed individual. The lining of the uterus superficially resembles 

 that of the mouth but has more glands and blood vessels and is physiologically 

 responsive to the embryo and to certain endocrine secretions. It takes part 

 in the formation of the maternal part of the placenta, the organ through 

 which the bodies of mother and child cooperate in the growth and develop- 



