478 



ZOOLOGY 



SECT. 



ducts a prominence, the teat (Fig. 1115), the wall of which may be 

 formed of the mammary pouch area alone (Marsupials, Kodents, 

 Primates), or, with greater or less reduction of the latter, mainly 

 from the surrounding integument. In the latter case the teat 

 may have a wide central canal. The number and situation of the 

 teats vary in the different groups, and have been noticed in the 

 synopsis of the characters of the orders and sub-orders (pp. 464 

 to 473). 



The two genera of the Prototheria, Ornithorliynchus and Echidna, 

 differ somewhat widely from one another in general appearance. 

 The former (Fig. 1116) has the surface covered with a close, soft 

 fur, and has the upper jaw produced into a depressed muzzle, 

 not unlike the beak of a duck, covered with a smooth, hairless 



FIG. 1115. Diagrams of the phylogenetic development of teats, a, primitive condition corre- 

 sponding to the condition in Echidna ; b, Wallaby (Ualmaturus) before lactation ; c, 

 Opossum (Didelphi/s) before lactation ; il, Opossum during lactation ; this diagram 

 stands also for the Mouse and Man ; c, embryonal, and/, full-grown cow. 1, integumentary 

 wall ; 2, mammary area, the broken line represents the mammary pouch ; 3, milk-ducts. 

 (After Max Weber.) 



integument, which forms a free fold or flap at the base. The 

 eyes are very small, and there is no auditory pinna. The legs 

 are short, and the five digits end in strong claws, and are con- 

 nected together by a web, so that the limbs are equally adapted 

 for burrowing and for swimming. The tail is elongated and 

 depressed, and is covered with fur. The male has a sharp-pointed, 

 curved spur on the inner side of the foot, having the duct of a 

 gland opening at its apex. Echidna (Fig. 1117) has the body 

 covered above with strong, pointed spines, between which are coarse 

 hairs ; the lower surface is covered with hair only. The jaws are 

 produced into a rostrum, which is much narrower than that of 

 Ornithorhynchus. The eyes are small, and there is no auditory 

 pinna. The limbs are short and powerful. There are five toes on 

 each foot, each ending in a very strong claw, by means of which 

 the Echidna is able to burrow with rapidity. There is a spur on 



