708 



MAMMALIA. 



Fig. 326. 



a 



that the ovaria, notwithstanding their racemose appearance, ex- 



hibit all the essential characters of the Mammiferous type of struc- 



ture ; and corpora lutea were formed where the reproductive germs 



had escaped from them. Secondly, that the eggs contained in 



the uterine cavities (Jig. 



327, c, e) had no con- 



nection whatever with the 



walls of the uterus. 



Thirdly, that each ovum 



exhibited the usual parts 



of an egg, viz. the cor- 



tical membrane, the al- 



bumen, and the yolk ; and 



that upon the latter a 



membrana vitelli and the 



blastoderm or germinative 



membrane were plainly 



perceptible. Fourthly, 



that the uterine walls 



assume an increased thick- 



ness when in an impreg- 



nated state, but that not 



the slightest trace of a 



decidual or adventitious 



membrane is apparent in 



the cavity of the womb. 



From all these circumstances, the distinguished author of the 



paper referred to* was led to adopt the subjoined train of rea- 



soning as to the probability of the Ornithorynchus being a vi- 



viparous Mammal. The form, the structure, and the detached 



condition of the ova, observes Professor Owen, may still be re- 



garded 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 



* On the Ova of the Ornithorynchus paradoxus, by Richard Owen, Esq. Phil. 

 Trans. Part II. for 1834, page 563. 



