682 



MAMMALIA. 



embryos of some Placentals also. In Ornithorhynchus, 

 the ischia form a long ventral symphysis ; in Echidna, the 

 acetabulum socket for the femur is incompletely ossified as 

 in Birds ; the pubes bear epipubic bones, as in Marsupials. 

 On the side of the tarsus, in the duckmole, there is a spur 

 perforated by the duct of a gland. This spur persists in the 

 males, is rudimentary in the females. The male Echidna 

 has a similar but smaller spur. 



The brain is smooth, the cerebellum is not covered by 

 the cerebrum, there is a large anterior commissure and the 

 corpus callosum is rudimentary, or, according to Symington, 

 absent. 



The food canal ends in a cloaca. 



The right auriculo-ventricular valve in Ornithorhynchus 

 is partly muscular as in Birds, 

 while in other Mammals it is 

 membranous and is worked by 

 papillary muscles attached to it 

 by tendon-like cords (chordae 

 tendineae). The temperature of 

 the body is said to be about 

 25-28 C. 



The ureters open, not into the 

 bladder, but into the urinogenital 

 canal. 



The testes remain in the abdo- 

 men. 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 attached to the ventral wall of the cloaca, and its canal is 

 not continuous with the urinogenital canal. 



The ova are large, with abundant yolk, and undergo 

 meroblastic segmentation. The Prototheria are oviparous. 



The duckmole, duck-billed platypus, or water mole, 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. It collects small animals in its 

 cheek pouches, and chews them at leisure with its eight horny jaw 



FIG. 244. Pelvis of Ech- 

 idna. (From Edinburgh 

 Museum of Science and Art.) 



S, sacrum ; Ep, epipubic bones ; 

 Ac, acetabulum ; o.f, obturator 

 foramen between ischium and 

 pubis (/.) 



