1 6 MARSUPIUM AND MAMMARY POUCH 



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 Echidna 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 Ehalanger 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 Echidna. 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) 



^ See Haacke, "On the Marsupial Ovum, the Maniuiary Pouch, etc., of the 

 Echidna," Proe. Roy. Soc. 1885, p. 72 ; and " tjber die Entstehungder Siiugetiere," 

 Biol. Ccntralhl. viii. 1889, p. 8. 



- See Gegenbaur's Elements of Comj). Anat. Transl. l>y Bell, 1878, p. 421. 



^ " Uber die Beziehungen zwischen Mannnartasche u. Marsupium,"' Morph. 

 Jalirh. xvii. 1891, p. 483. 



