446 



ZOOLOGY 



SECT. 



On its ventral wall is a small, hard, rod-like body, the clitoris (c. c.), 

 corresponding to the penis of the male, and composed of two 

 very short corpora cavernosa attached anteriorly to the ischia, with 

 a terminal soft conical glans clitoridis (g. cL). The vulva, or external 

 opening of the vestibule, is bounded laterally by two prominent 

 folds the labia majora. 



Development. The Rabbit is viviparous. The ovum, which 

 is of relatively small size, after it has escaped from its Graafian 

 follicle, passes into the oviduct, where it becomes fertilised, 

 and reaches the uterus, in which it develops into the foetus, 

 as the intra-uterine embryo is termed. The young animal 



escapes from the uterus in 

 a condition in which all 

 the parts have become 

 fully formed, except that 

 the eyelids are still closed, 

 and the hairy covering is 

 not yet completed. As 

 many as eight or ten young 

 are produced at a birth, 

 and the period of gesta- 

 tion, i.e., the time elapsing 

 between the fertilisation 

 of the ovum and the birth 

 of the young animal, is 

 thirty days. Fresh broods 

 may be born once a month 

 throughout a considerable 



FIG. 1036. Diagrammatic longitudinal section of a part of the year, and, as 



Rabbit's embryo at an advanced stage of pregnancy. fTi^ ATrmnn* TJoKKif TV>OI^ 



a. amnion; a, urachus ; al. allantois with blood- Lne . y Un g . tt&Dt Hia^ 



vessels, ds, cavity of yolk-sac ; e. embryo; erf. endo- begin breeding at the age 



dermal layer of yolk-sac ; cd'. inner portion of endo- f , 



of three months, the rate 

 of increase is very rapid. 



The segmentation is of 

 the holoblastic type. An 

 amnion and an allantois 

 are developed much as in the case of the Bird (p. 412). But the 

 later history of these foetal membranes is widely different in the 

 bbit, owing to the modifications which they undergo, in order 

 to take part in the formation of the placenta the structure by 

 whose instrumentality the foetus receives its nourishment from 

 the walls of the uterus. The placenta is formed from the serous 

 membrane, or outer layer of the amniotic fold, in a limited disc- 

 shaped area, in which the distal portion of the allantois coalesces 

 with it. The membrane thus formed (chorion) develops vascular 

 processes the chorionic villi which are received into depressions 

 (the uterine crypts) in the mucous membrane of the uterus. The 



derm ; ed". outer portion of endoderm lining the com- 

 pressed cavity of the yolk-sac ; fd. vascular layer of 

 yolk-sac ; pi. placental villi ; 7*. space filled with fluid 

 between the amnion, the allantois and the yolk- 

 sac ; sh, subzonal membrane ; st. sinus termiiialis. 

 (From Balfour, after Biechoff.) 



