XIII 



PHYLUM CHORDATA 



475 



The oviducts in the anterior part of their extent (Fallopian 

 tubes, fl.t.\ are very narrow and slightly convoluted. They open 

 into the abdominal cavity by wide funnel-shaped openings (fl.f .} 

 with fimbriated or fringed margins. Posteriorly each passes into 

 a thick-walled uterus (r. ut.\ The two uteri open separately into 

 a median tube, the vagina (vet.). The vestibule (Fig 1097, vb.\ or 

 urinogenital canal, is a wide median passage, into which the 

 vagina and the bladder 

 open. On its ventral wall 

 is a small, hard, rod-like 

 body, the clitoris (c. c.) 

 with a pointed apex 

 (g. cl.\ corresponding to 

 the penis of the male, and 

 composed of two very 

 short corpora cavernosa 

 attached anteriorly to the 

 ischia, and invested in- 

 ternally by a soft, grooved 

 corpus spongiosum. The 

 vulva, or external open- 

 ing of the vestibule, is 

 bounded laterally by two 

 prominent folds the 

 labia major a. 



Development. The 

 Rabbit is viviparous. The 

 ovum, which is of re- 

 latively small size, after 

 it has escaped from its 

 Graafian follicle, passes 

 into the oviduct, where 

 it becomes fertilised, and 

 then 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 gestation, 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 part of the year, and, as the 

 young Rabbit may begin breeding at the age 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. 440), 

 But the later history of these foetal membranes is widely different 



G G 2 



FIG. 1099. Diagrammatic longitudinal section of a 

 Rabbit's embryo at an advanced stage of pregnancy, 

 a. amnion ; a, stalk of allantois ; al. allantois with 

 blood-vessels ; ds, cavity of yolk-sac (umbilical 

 vesicle) ; e. embryo ; ed. endodermal layer of yolk- 

 sac ; ed'. inner portion of endoderm ; ed". outer 

 portion of endoderm lining the compressed cavity of 

 the yolk-sac ; fd. vascular layer of yolk-sac ; pi. 

 a placental villi ; r. space filled with fluid between 

 the amnion, the allaiitois and the yolk-sac ; sh, sub- 

 zonal membrane ; st. sinus terminalis. (From 

 Balfour, after Bischoff.) 



