836 



PHYLUM CHORDATA I CLASS MAMMALIA 



The food canal ends in a cloaca. 



The right auriculo-ventricular valve in Ornithorhynchiis 

 is partly muscular as in Birds, while in other Mammals it 

 is membranous and worked by papillary muscles attached 

 to it by tendon-like cords (chordae tendineae). The 

 temperature of the blood is about 25^-28° C, and is note- 

 worthy in being unusually variable. In fact, the Mono- 

 tremes are imperfectly warm blooded. 



The ureters open, not into the bladder, but into the 

 urinogenital canal, as in the embryos of higher Mammals. 



The testes remain in the abdomen. The left ovary is 

 larger than the right, as in Birds. The vasa deferentia open 



separately into the urinogenital 

 canal. So in the female do the 

 oviducts, and these have no fringed 

 fimbriated apertures nor distinct 

 uterine region. The penis is at- 

 tached to the ventral wall of the 

 cloaca, and the urinogenital canal 

 communicates both with the cloaca 

 and with the canal of the penis. 

 The whole structure resembles in 

 many ways the copulatory organ 

 of certain Reptiles and Birds. 



The ova are large, with abund- 

 ant yolk, and undergo meroblastic 

 segmentation. The Prototheria 

 are oviparous. 



Fig. 500. — Pelvis of 

 Echidna. 



S., Sacrum ; Ep., epipubic 

 bones ; Ac, acetabulum ; 

 o.f., obturator foramen 

 between ischium and pubis 



iP-)- 



, The duckmole, or duck-billed platypus, lives beside lakes and rivers. 

 It swims by means of its fore-limbs, which are webbed as well as 

 clawed ; it grubs for aquatic insects, crustaceans, and worms, in the 

 mud at the bottom of the water or among the floating weeds. It 

 collects small animals in its cheek pouches, and chews them at leisure 

 with its eight horny jaw-plates. It makes long burrows in the banks, 

 often with two openings, one above, one under the water. The animal 

 is shy, and dives swiftly when alarmed. When about to sleep, it rolls 

 itself into a ball. In the recesses of the burrows the eggs are laid, two 

 at a time. The egg measures about three-quarters of an inch in length, 

 and is enclosed in a flexible white shell, through which the young 

 animal has to break its way. 



The full-grown duckmole measures from 18 to 20 in. in length ; the 

 male slightly exceeds his mate. The fur is short and soft, dark brown 

 above, lighter beneath. The jaws are flattened like the bill of a duck, 



