MR. OWEN ON THE OVA OF THE ORNITHORHYNCHUS PARADOXUS. 657 



Ornithorliynchus preserved in the Military Museum at Chatham^, I subsequently 

 found three ovisacs developed in the ovary to a similar but not greater extent. Mr. 

 HiLL-f, who first detected the ovarian ova in the recent animal, also states that they 

 were not larger than a small pea ; and they have never exceeded that size in any of 

 the specimens examined by Sir Everard Home. 



A knowledge of the size which the ovarian ovum of the Ornithorhjnichus ac- 

 quires before it finally escapes, is of great consequence in forming a judgement as 

 to the ultimate mode of development of the embryo, as a direct deviation from the 

 generation of the ordinary Mammal, and a proportional approximation to that of the 

 Bird, would be manifested in the ratio of the accumulation of the vitelline matter in 

 the ovisac. Now it has very recently been supposed that the ovulam of the Ornitho- 

 rhynchus attains a greater diameter than in other Mammalia before passing from 

 the ovary; and Professor De Blainville;}: adduces in favour of this opinion the 

 size of the ova discovered by Lieutenant Maule, and the corresponding capacity of 

 the orifice of the Fallopian tube. But the expression of the zealous officer just alluded 

 to, leads to the belief that the eggs of the size of a large musket-ball which he saw, 

 were in the uterus rather than in the ovary; and the size of the orifice of the Fal- 

 lopian tube in Mammalia is in relation with that of the entire ovary which it em- 

 braces, and not with that of the ovum which it is destined to transmit to the 

 uterus. 



The two ovarian ova or ovisacs § were two lines and a half in diameter, and ad- 

 hered to the ovary by about one third part of their whole circumference. 



In the specimen in the Chatham Museum the three ovisacs which had attained 

 nearly the same size, were attached to the ovary by a smaller portion of their circum- 

 ference, but were still sessile, and not appended, as in the Bird, by a distinct pedicle. 

 In both specimens smaller ovisacs of different sizes projected to a greater or less 

 extent from the surface of the ovary. 



The clustered form of the ovary, which results from this position of the ovisacs, is 

 not, however, peculiar to the Ornithorhynchus among Mammalia, but obtains in a 

 greater or less degree throughout the Marsupial and Rodent orders. De Graaf long 

 ago figured the ovary of the Rabbit as composed, when prepared for impregnation, 

 like that of the Ornithorhynchus, of a cluster of spherical ovisacs or foUiculi || ; and 

 Daubenton, in describing the ovaria of the Black Rat^ and of the Water Rat**, 

 particularly notices their tubercular or racemose figure, and the yellow colour of the 



* My thanks are especially due to G. J. Gxtthrie, Esq. F.R.S., and to the officers in charge of the Museum 

 at Fort Pitt, for the facilities there afforded me in the examination of this specimen. 



t Transactions of the Linnean Society, vol. xiii. p. 623. 



X Nouvelles Ahnales du Museum, tom. ii. p. 405. 



§ Philosophical Transactions, 1832. Plate XVI. 



II De Mulierum Organis, Tab. xxv. p. 412. Opera Omnia, Lugd. Batav. 1677. 



^ BufFon, Hist. Nat., tom. vii. Plate xxxviii. p. 293. 



** Ibid., Plate xlvi. p. 357. 

 MDCCCXXXIV. 4 C 



