682 



DESCRIPTION (WITH FIGURES) OF A YOUNG SPECI- 

 MEN OF OR?iITHORHYNCHUS ANATINUS FROM 

 THE COLLECTION OF THE AUSTRALIAN MUSEUM, 

 SYDNEY. 



By J. T. Wilson, M.B., Peofessok of Anatomy in the 

 LTniversity of Sydney. 



(Plate xlix. ) 



Opportunities of studying the anatomy of young ("foetal"') 

 specimens of Ornithorhynchus have seldom occurred to the scien- 

 tific investigator, if we may judge from the paucity of published 

 descriptions of such specimens. 



The explanation of this fact is obvious enough if we remember 

 that the eggs of the animal are laid while the development of the 

 embryo is yet at a very early stage (according to Caldwell* at a 

 stage equivalent to that of a 36 hours' chick, and that the 

 further development, both within the egg and probably for a 

 prolonged period after hatching, goes on in the nest situated at the 

 end of a lengthy burrow which is rather difficult of discovery and 

 by no means easy of access. 



In consequence of the al)sence Ijoth of pouch and of teat in the 

 platypus, the young animal during the period of development 

 which answers to that of the "mammary foetus" of the marsupial, 

 is probably either wholly unattached or only very insecurely and 

 temporarily attached to the person of the mother. Thus, even if 

 the latter emerges at all from the burrow during the period of 

 nurture of her offspring, as is likely enough, it is improbable that 

 she bears her young about with her. That she should do so 

 habitually is indeed excluded by the aquatic habits of the species. 

 The capture of adult females in a state of lactation has been 

 recorded, but the young naked "mammary foetus" has never been 

 obtained save in the nest. In this respect the habit of the 



♦Caldwell : Journ. & Proc. Roy. Sou. N.S.VV. xviii. p. 117. 



