16 MARSUPIUM AND MAMMARY POUCH CHAP. 
supials.' It is usually held that this structure is not of pre- 
cisely the same morphological value as the pouch of the 
Marsupial; and the difference is expressed by terming the one 
(that of Echidna) the mammary pouch, and the other the 
marsupium. At first sight it may appear to be an unnecessary 
refinement to separate two structures which have so many and 
such obvious likenesses. It is not quite certain, however, that the 
difference is not even more profound than later opinions seem 
to indicate. The Monotremata not only have no teats, as has 
already been pointed out, but the mammary glands themselves 
are of a perfectly different nature to those of the higher mammals, 
including the Marsupials. There is therefore no a priori 
objection to the view that the accessory parts developed in con- 
nexion with the mammary glands should also be different. The 
teat of the higher Mammalia grows up round the area upon 
which the ducts of the mammary glands open; it is a fold of 
skin which eventually assumes the cylindrical form of the adult 
teat, and which includes the ducts of the milk glands. It has 
been suggested that the two folds of skin which form the 
mammary pouch of Hehidna are to be looked upon as the equi- 
valent of the commencing teat of the higher mammal.’ In this 
case it is clear that the marsupial folds of the Marsupial cannot 
correspond accurately with the apparently similar folds of 
Echidna, because there are teats as well. It is the teats which 
correspond to the marsupial folds of Echidna. This view is in 
apparent contradiction to an interesting discovery in a specimen 
of a Phalanger by Dr. Klaatsch.’ This Marsupial, like most 
others, has a well-developed marsupial pouch, in which the 
young are lodged at birth; but round two of the teats is 
another distinct fold on either side, the outer wall of which 
forms the general wall of the pouch. Dr. Klaatsch thinks 
that these smaller and included pouches are the equivalents of 
the mammary pouches of Lehidna. They contain teats, but this 
comparison does not do away with the validity of Gegenbaur’s 
suggestion already referred to, because the teats are (see above) ¢ 
1 See Haacke, ‘‘On the Marsupial Ovum, the Mammary Pouch, etc., of the 
Echidna,” Proc. Roy. Soc. 1885, p. 72; and ‘‘ Uber die Entstehung der Saugetiere, ” 
Biol. Centraibl. viii. 1889, p. 8. 
2. See Gegenbaur’s Llements of Comp. Anat. - Transl. by Bell, 1878, p. 421. 
3 Uber die Beziehungen zwischen Mammartasche u. Marsupium,” Morph. 
t=) r] 
Jahrb. xvii. 1891, p. 483. 
