822 



MAMMALIA. 



Fig. 415. 



organization which appear to be essential to successful incubation, viz. a 

 voluminous yelk to support the germinal membrane, and the mechanism 

 for bringing the cicatricula into contiguity with the body of the parent. 

 Add to this, that such a mode of development of the foetus requires that 

 all the necessary nutritive material be accumulated in the ovum prior to 

 its exclusion. Now the bony pelvis of the Bird is expressly modified to 

 allow of the escape of an egg, both large from the quantity of its con- 

 tents, and unyielding from its necessary defensive covering : but, what- 

 ever affinities of structure may exist in other parts of the Ornitho- 

 rhynchus, it is most important to the question of its generation to bear 

 in mind that it manifests no resemblance to the Bird in the disposition 

 of its pubic bones. 



(2427.) From the above considerations it is therefore probable that 

 the young Ornithorhynchi are produced alive ; yet still the reader will 

 perceive, by the closeness of the reasoning brought to bear upon the 

 subject, how nearly the oviparous and mammiferous modes of generation 

 are approximated by the interposition of these connecting forms of 

 Vertebrata. 



(2428.) But if from these arguments, derived from the anatomical 

 construction of the female parts, it is 

 allowable to conjecture that the Orni- 

 thorhynchus is ovoviviparous (using 

 that term in a strictly philosophical 

 sense), the difficulties of the case are 

 by no means removed ; and granting 

 that the contents of the ovum are 

 barely sufficient to nourish the embryo 

 during the very earliest stages of its 

 development, we have yet to learn 

 how the foetus is matured after the 

 exhaustion of this supply. There is 

 no reason whatever to suppose that a 

 placenta exists at any period of uterine 

 gestation; neither is there a mar- 

 supial pouch in which the prema- 

 turely-born young can, be carried 

 about and supplied with milk; so 

 that, whether the young Monotreme 



be developed in the uterus or out of the uterus, we are equally at a loss 

 to understand how its nutrition is provided for. 



(2429.) In this state of uncertainty, the anatomy of the young Orni- 

 thorynchus, examined at as early a period as possible, becomes a subject 

 of extreme interest ; and fortunately Professor Owen has been enabled 

 to add observations upon this subject to his other valuable researches 



Young Ornithorhynchus. 



