THE MAMMALIA 



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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. 

 a^, allantoic stalk ; Bl, bladder ; cc, corpus cavernosum ; c.e^, caput 

 epididymis ; ep, epididymis ; g-c, Gartner's canal'; /:»?, hydatid of Morgagni, 

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

 ov, ovary ; ^£', perineal gland ; ^o^, paro-ophoron ; ^.ov, paro-varium these two 

 representing the Wolffian body in the female ; Ji, rectum ; T, testis ; tcr, ureter ; 

 jci, uterus; utA, urethra; u^tji, uterus masculinus ; vag; vagina; F(/, vas 

 deferens ; z/.^/J vasi. efFerentia ; vi, 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 



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