THE MAMMALIA 



299 



The lowest mammalia, the Prototheria, are oviparous, and 

 lay eggs furnished with a large quantity of food-yolk. In all 

 other mammalia the ova are very small, are practically devoid 

 of food-yolk, and undergo a total segmentation. The embryo 

 is retained for a longer or shorter time in the uterus of the 

 mother, is attached to the uterine walls, and is nourished by 

 the agency of the maternal blood-vessels. The embryonic 

 organ by which the embryo is attached to the uterine walls is 



Fig. 74 



Diagrams of the urogenital system of mammals, that of the male on the left, of 

 the female on the right. The prostate and Cowper's glands are omitted. 

 as, allantoic stalk*; Bl, bladder ; cc, corpus cavernosum ; c.ep, caput 

 epididymis ; ep, epididymis ; gc, Gartner's canal ; hm, hydatid of Morgagni, 

 representing the upper end of the oviduct ; od, Fallopian tube or oviduct ; 

 ov, ovary ; pg, perinea! gland ; pop, paro-ophoron'; p.ov>, paro-varium these two 

 representing the Wolffian body in the female ; /?, rectum ; 7", testis ; ur, ureter ; 

 ut+ uterus ; uth, urethra; utm, uteru> masculinus ; vag, vagina; V d, vas 

 deferens ; v.ef, vas\ effereniia ; vt, vestibule. 



known as the placenta. In the Metatheria or Marsupials, in- 

 cluding the kangaroos, wombats, opossums, etc., the young are 

 born very early, and are carried while in a helpless state in a 

 special pouch or marsupium situate on the abdomen of the 

 mother. Nevertheless, a more or less intimate placental 

 attachment is effected between the embryo and the uterine 



