1 8 VESTIGIAL POUCHES CHAP. 



opens backwards is less disadvantageous to the contained 

 young. 



The male Thylacine has a pouch which is quite or very 

 nearly as well formed as in the female. There are also rudi- 

 ments of a pouch in the male foetuses of many Marsupials, 

 especially of those belonging to the Polyprotodont section of the 

 order, though these rudiments are by no means confined to that 

 subdivision. Up to so late a period as the age of four months 

 (length 19 '8 cm.) the male Dasyurus ur sinus has a pouch. 



We have now to consider the interesting series of facts 

 relative to the permanence in a rudimentary condition it is 

 true of the mammary pouch in the higher Mammalia, facts 

 which seem to be an additional proof that they have been 

 derived from an ancestor in which the pouch was an organ of 

 functional importance. The first definite proof of the occurrence 

 of a pouch in any mammal not a Marsupial or a Monotreme was 

 made by Malkmus, who found this structure in a Sheep. It 

 seems, however, that the structures found in the higher mammals 

 are not always comparable to the marsupiurn of the Marsupials, 

 but sometimes to the mammary pouch of the Monotreme. That 

 the Marsupials are a side line, and not involved in the ancestry 

 of the Eutheria, is an opinion which is at present widely held. At 

 the same time it is reasonable to suppose that the original stock 

 lying between the Prototheria and the Metatheria, whence the 

 latter and the Eutheria have arisen, preserved both the mammary 

 pouch of the lower mammal and the marsupiurn of the further- 

 developed stage, as docs Phalangista occasionally at the present 

 day. Hence to find remnants of both structures in existing 

 mammals would not be incredible. This is what Dr. Klaatsch 

 believes to be the case. In certain Ungulates, including two 

 species of Antelope, Dr. Klaatsch found very considerable rudi- 

 ments of folds provided with unstriated muscular fibre ; there 

 were in the adult Cervicapra isabellina a pair of pouches, one on 

 each side, and a rudiment of a second on either side ; possibly 

 this multiplication of the pouches has relation to the number of 

 young. That there is more than one pouch makes a comparison 

 with the mammary pouch rather than with the marsupium 

 probable. The Ungulate teat, it must be remembered (see p. 16), 

 is a secondary teat ; hence there is no difficulty in the com- 

 parison from this point of view. A pouch containing a primary 



