OENITHOEHYNCHUS PAKADOXTJS. 821 



reasoning as to the probability of the Ornithorhynchus being a vivipa- 

 rous mammal. The form, the structure, and the detached condition of 

 the ova, observes Professor Owen, may still be regarded as compatible 

 with, and perhaps favourable to, the opinion that they are excluded as 

 such, and that the embryo is developed out of the parent's body. But 

 the following objections present themselves to this conclusion : The 

 only part of the efferent tube of the generative apparatus which can be 

 compared in structure or relative position with the shell-secreting uterus 

 of the Fowl is the dilated terminal cavity in which, in all the specimens 

 examined, the ova were situated : and upon the oviparous theory it must 

 be supposed either that the parietes of this cavity, after having secreted 

 the requisite quantity of soft material, suddenly assume a new function, 

 and complete the ovum by providing it with the calcareous covering 

 necessary to enable it to sustain the superincumbent weight of the 

 mother during incubation ; or that this is effected by a rapid deposition 

 from the cuticular surface of the external passages ; or lastly, according 

 to a more recent but still more improbable supposition, by a calcareous 

 secretion of the abdominal glands poured out upon the ovum after its 

 exclusion. 



Fig. 414* 



Ovaria of Ornithorhynchus parddoxus. 



(2426.) But granting that the egg is provided in any of these ways 

 with the necessary external covering, yet, from the evidence afforded 

 by the specimens examined, the ovum is deficient in those parts of its 



* Owing to an error on the part of the draughtsman, who has neglected to reverse 

 the drawing, the left uterus in the above figure is represented on the right side, and 

 vice 



