CHAPTER XIV 



DEVELOPMENT OF LEPUS (THE RABBIT) 



Fertilisation. — The egg is very small, and contains very little 

 yolk. It is surrounded by a vitelline membrane secreted by 

 itself, and by a secondary membrane formed from the follicle- 

 cells, the zona pellucida. The follicle-cells are several layers 

 thick surrounding each egg- cell, which however they do not 

 fit closely. There is a large space inside the follicle filled with 

 fluid and bathing the egg t which gives the characteristic 

 appearance of the Graafian follicle, typical of mammals. One 

 polar body is extruded in the ovary, the second is extruded 

 after fertilisation. 



Ovulation is the process of escape of the egg from the 

 ovary. The follicle vacated by the tgg becomes filled by the 

 great increase in size of the follicular cells and by the ingrowth 

 of connective tissue and blood-vessels, and becomes a corpus 

 luteum. Should the egg just ovulated be fertilised, the 

 corpus luteum becomes an important structure, functioning as 

 a gland of internal secretion, and among its functions are the 

 following. It prevents ovulation of other eggs during the 

 period of pregnancy, it stimulates the uterus to hypertrophy 

 and so prepares for the reception and fixation of the embryo, 

 and it stimulates the mammary glands to secrete. The corpus 

 luteum disappears at the end of the period of gestation, but if 

 no pregnancy has ensued it disappears soon after ovulation. 



Many mammals ovulate spontaneously during periods of 

 " heat," or oestrus, and the mouse is among them. Others, such 

 as the rabbit, only ovulate after copulation. During copulation 

 sperms are introduced into the vagina, and they make their 

 way up through the uteri to the oviducts, near the top of which 



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