358 MR. OWEN ON THE GENERATION OF THE MARSUPIAL ANIMALS. 



those above described, and having been successfully injected, showed that the vaginae 

 were highly vascular. The history of this female is not known, but this additional 

 example of the presence of mucus with fibrous masses in the vaginae would intimate 

 that it is not an uncommon occurrence, and therefore unlikely to be the result of 

 disease. 



I had originally intended to limit myself to the description of the preparation 

 which first called my attention more directly to the subject ; but the desire of pe- 

 netrating, if possible, to the final purpose of marsupial generation, induced me to 

 push my inquiries as far as the means at my disposal allowed ; and though I am com- 

 pelled to acknowledge that the end proposed is still to be attained, yet the collateral 

 inquiries instituted with that view have, I hope, tended to render the subject more 

 intelligible, and to point out its real analogies to other known modes of generation. 



The conditions of those modifications of structure which relate to the mar- 

 supial foetus after uterine birth are readily appreciable. An offspring prematurely 

 born, and with a great proportion of its growth yet to be accomplished before it 

 attains the power of existing independently, must obviously be incapable of sustain- 

 ing life with any considerable intermission of sustenance ; and since it has no store 

 of nutriment appended to its digestive canal when excluded from the womb, and is 

 therefore dependent for its support solely upon maternal secretion, the period during 

 which the mother must have been confined to a foreign and artificial nest, supposing 

 no other protection to the offspring had been provided, would have been probably 

 too long to be compatible with her own existence. To obviate this inconvenience a 

 natural and portable nest is superadded to her structure, in order that she may 

 resort, without prejudice to the young, to all the places necessary for her own 

 safety and support ; while at the same time the young one is enabled to draw an 

 unintermitting supply of nutriment, and has also its own temperature maintained by 

 close contact with the abdominal surface of the parent, in an analogous, though more 

 complete manner than the egg during incubation. 



But when we come to consider why the intra-uterine life of the embryo should be 

 such, both in its nature and duration, as to require these modifications, the subject, 

 at present, eludes every attempt at direct explanation. If an unvascular chorion, 

 with the consequent premature birth and after-incubation in a marsupium, were 

 peculiar to the Kangaroo, these might be regarded as the necessary concomitant 

 phenomena of its strange proportions and violent progressive motion; it might 

 then be considered essential that the foetus should pass the pelvis before the hinder 

 parts had attained their gigantic proportions ; it might also be supposed that saltatory 

 progression was incompatible with the safety of the parent or offspring, if the foetus 

 were attached to the womb by so delicate but vital a medium as a vascular placenta ; 

 and that, therefore, while a premature birth obviated the necessity for the formation 

 of a placenta, an unimpeded delivery was equally secured by the same anticipation. 



