188 5.J Mammary Pouch, fyc, of Echidna hystrix. 73 



The JEchidna egg, when taken out of its mother's pouch, unfortu- 

 nately burst, and it was found to be almost wholly decomposed inside. 

 The mother having been worried by being captured and during 

 captivity accounts for the state the egg was found in. As the shell 

 of the egg broke so soon I am unable to give the egg's dimensions 

 as accurately as could be desired ; however, I think I am nearly 

 correct in stating its length as 15 m.m., and its width as 13 mm. ; 

 it will thus be seen that the egg is nearly globular in shape. In a 

 preliminary notice to the " Zoologischer Anzeiger " the dimensions 

 given are somewhat incorrect. 



The shell of the egg was parchment-like, like that of the eggs of 

 many reptiles. Its outer surface was considerably smoother than the 

 inner one. Its thickness was about \ mm. 



The inner surface of the egg-shell was covered with a loose mem- 

 brane which on microscopical examination showed a network of what 

 I supposed to be blood-vessels ; no other trace of an embryo could be 

 discovered. 



It will have been observed already that I speak of one "mammary 

 pouch " or " marsupium " only, whereas Professor Owen described as 

 pouches two semilunular fossae, at the fundi of which he found the 

 orifices of the mammary glands (" Phil. Trans.," vol. 155). But as 

 the mammary pouch serves at one period as an incubator for the 

 " marsupial ovum," it must at least at this time have a shape enabling 

 it to undertake this function. Accordingly, we find in my specimen 

 one deep pouch large enough to hold, although not wholly to conceal, 

 a gentleman's watch, having its fundus in the median plane of the 

 body towards the cloaca, and running out into shallower fossae 

 towards the mammary areolae, beyond which towards the anterior 

 end Of the body it gradually disappears. The skin forming the 

 pouch is thinner than that of the rest of the ventral integument, 

 and the pouch and its lips are covered more thinly with hair, the 

 latter being shorter, however, and standing thicker on the mammary 

 areolae, where very conspicuous tufts of hair are easily to be observed. 

 Although the marsupial integument is devoid of subcutaneous muscles, 

 the animal can considerably modify the shape of the pouch, probably 

 by the surrounding integumentary muscles. 



Quite recently Professor Gegenbaur ("Morphologischer Jahrbuch," 

 1884) examined two adult females of 'Echidna setosa for the existence 

 of mammary pouches, but without success. He, therefore, inclines 

 to think that the pouches are only periodically developed organs. 

 Although I have not sufficient evidence to prove this supposition, I 

 believe it is the correct one ; how could the statements of Professor 

 Owen, of Professor Gegenbaur, and of myself otherwise be reconciled ? 

 I believe the pouch attains its greatest development during the time 

 it serves as incubator for the egg, and it consists of a pair of semi- 



