820 



MAMMALIA. 



Fig. 413. 



little pouch in the floor of the cloaca, from which it projects when 

 erected. 



(2423.) The cloaca! cavity, as in birds, gives passage to the faeces and 

 to the urine. The testes (fig. 412, a) and the vasa deferentia (b) re- 

 semble those of an oviparous animal ; but, on the other hand, there is 

 a complete urinary bladder (c), and moreover a pair of auxiliary (CWper's) 

 glands (d d), organs never met with except in the Mammiferous class. 



(2424.) The anatomy of the female organs is not less singular. The 

 ovaria (fig. 414, a a) are large and racemose, like those of a bird ; while 

 the two oviducts or uteri (fig. 413, a a), as the reader may choose to call 

 them, open into the cloaca 

 by two distinct orifices (c c), 

 situated on each side of the 

 urethra, derived from the 

 bladder (6). 



(2425.) It is to Professor 

 Owen that science is indebted 

 for all that is known relative 

 to the anatomy of the female 

 Ornithorhynchus when in a 

 gravid state; and his re- 

 searches upon this subject ap- 

 pear to establish the follow- 

 ing interesting particulars : 

 First, that the ovaria, not- 

 withstanding their racemose 

 appearance, exhibit all the 

 essential characters of the 

 Mammiferous type of struc- 

 ture ; and corpora lutea were 

 formed where the reproduc- 

 tive germs had escaped from 

 them. Secondly, that the 

 eggs contained in the uterine 

 cavities (fig. 414, c, e) had no connexion whatever with the walls of the 

 uterus. Thirdly, that each ovum exhibited the usual parts of an egg, 

 viz. the cortical membrane, the albumen, and the yelk ; and that upon 

 the latter a membrana mtelli and the blastoderm or germinative mem- 

 brane were plainly perceptible. Fourthly, that the uterine walls assume 

 an increased thickness when in an impregnated 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 



* " On the Ova of the Ornithorhynchus paradoxus," by Richard Owen, Esq., 

 Phil. Trans, pt. ii. for 1834, p. 663. 



Generative organs of female Ornithorhynchus. 



