124 



MARSUPIAL " LARVAE " 



are the precise et^iiivalents of similar lioiies in the Monotremata. 

 It has been held, but apparently erroneously, that these bones 

 are mere ossifications in the tendons of the external oblique 

 muscle of the abdomen, or of the pyramidalis of the same region ; 

 and vestiges have been asserted to exist in the Dog. Such 

 bonelets are undoubtedly present in the 

 Dog ; but it seems clear from their de\'elop- 

 ment in Marsupials, as structures actually 

 continuous with the median unossified por- 

 tion of the symphysis pubis, that the 

 " marsupial bones " belong to that part of 

 the skeleton, and that they correspond with 

 the epipubis of certain amphibians and 

 reptiles. The pouch, it may be remarked, 

 exists in a rudimentary form in the males 

 of many Marsupials. 



The most salient feature in the life- 

 history of the ^Marsvipials is the imperfect 

 condition in which tlie young are born. 

 The egg is no longer 

 laid, as in the Mono- 

 tremes; but curiously 

 enough the ovum, 

 which has the small 

 size of that of the [ 

 Eutheria, divides in- \ 

 completely at the ^ 

 first division (as Mr. \ 

 ('aldwell has shown), 

 and this develop- 

 mental feature may 

 perhaps be looked 

 u})on as a reminiscence of a former large- 

 yolked contlition. The young when born 

 are small and nude ; the newly born young of a large Kangaroo 

 is perhaps as large as the little finger. The young are trans- 

 ferred by the lips of the mother to the pouch, where they are 

 placed upon a teat. It is an interesting fact that they are 

 not merely imperfect foetuses, but that they are actual larvae. 

 They possess in fact at any rate one larval organ in the shape of 



Flo. 60. — Ventnil surface of 

 innominate boue of Kan- 

 garoo {MacwjiK-s ituijor). 

 X J. a, Acetabulum ; ah, 

 acetabular border of ilium ; 

 is, iliac surface ; m, " mar- 

 supial " boue ; pb, pubic 

 border ; pt, pectineal tu- 

 bercle ; .s, symphysis ; si, 

 supra - iliac border ; ss, 

 sacral surface ; ihf, thy- 

 roid foramen ; //, tuber- 

 osity of ischium. (From 

 Flower's Osfeoloijtj. ) 



Fui. 61. — Mammary foetus 

 of Kangaroo attached to 

 the teat. (Nat. size.) 

 (From Parker and Has- 



well's Ziiologij.) 



