350 THE EABBIT. 



At this stage the egg is liberated, by rupture of the Graafian 

 follicle, and is taken up by the mouth of the oviduct. It is 

 invested by the thin vitelline membrane, outside which is the 

 much thicker zona radiata. More or fewer of the cells of the 



Fig. 134. Fig. 135. 



Fig. 134. — A fully formed ovum of a Babbit, shortly before its discharge from 



the ovary. (After BischofE.) x 200. 



Fig. 135. — A Babbit's ovum, from the upper end of the oviduct, after extrusion 



of the two polar bodies. (After BischofE.) x 200. 



MO, spermatozoon. M", uucleus or germinal vesicle. JTIT, nucleolna or germinal 

 spot. PB, polar bodies. Z, zona radiata. 



inner layer of the follicle usually remain adhering to the zona 

 radiata. 



After entering the oviduct, but before fertilisation is effected, 

 a second polar body, apparently not more than half the size of 

 the first one, is extruded from the egg (Fig. 135, pb). 



4. Ovulation. 



Throughout the warmer part of the year, there is a periodi- 

 cally recurring ripening and discharge of ova from the ovaries of 

 the doe rabbit. From April to July this periodic discharge, 

 which is spoken of as ovulation, occurs regularly, and at monthly 

 intervals : after July it usually takes place with less regularity. 



The total period occupied in the development of the young 

 rabbit, from fertilisation of the egg to the time of birth, is thirty 

 days : that is to say, the total period of development is in the 

 rabbit of the same length as the interval between two succes- 

 sive acts of ovulation. 



The ovary of the doe rabbit, at the time she gives birth to 

 young, usually contains fully formed Graafian follicles, with ripe 

 ova ready for discharge. As a rule the doe is impregnated by 



