MR. OWEN ON THE OVA OF THE ORNITHORHYNCHUS PARADOXUS. 559 



of the ovarian follicles or ovisacs in the Rabbit, — a difference which he considers to 

 be dependent on impregnation ; the ovisacs then becoming denser and of a redder 

 tinge until the ova escape, which takes place the third day after the coitus. 



From a comparison of the ovarian ovum of the Ornithorhynchus with the mature 

 ovarian ova of the Rabbit, the Sow, and the Ewe, the principal difference consists in 

 the greater proportion of granules in the contained fluid, and in the more coherent 

 nature of the external granular stratum, which however appears not to possess the 

 necessary consistence to be, with its contents, expelled entire from the ovisac. In 

 the Fowl, on the contrary, where there is no adhesion between the ovarian ovum and 

 the calyx, the former passes unbroken into the oviduct. Thus in every essential par- 

 ticular the monotrematous ovum up to this period of development is the same as 

 that of the ordinary Mammalia ; and its structure is in exact physiological corre- 

 spondence with the mode of nourishment of the young animal. 



Soon after the preceding observations had been made, three uteri of the Ornitho- 

 rhynchus, containing ova of different sizes, were transmitted from New South Wales 

 to the Museum of the Royal College of Surgeons, by my friend George Ben- 

 nett, Esq. F.L.S.* 



The Board of Curators having liberally granted me permission to describe and 

 figure these interesting preparations, I am enabled to resume the subject of the pre- 

 vious observations, and proceed with the description of the ovaries as they appear 

 after the impregnation and the escape of the ova into the uterus. 



In each of these specimens, the left ovary only had taken on the sexual actions, 

 but did not exceed in size the same parts in the unimpregnated specimens above 

 described. The right ovary had, however, become enlarged ; it measured half an 

 inch in length, a third of an inch in breadth, and was about half a line in thickness : 

 a few ovisacs, about the size of a small pin's head, projected from the surface. 



The left ovary in each of the specimens was concealed by the thin membrane, 

 forming the expanded orifice of the oviduct. In one of these it was with some diffi- 

 culty it could be withdrawn from the Fallopian aperture, owing to the adhesion which 

 was produced by what appeared to be a coagulated secretion ; a circumstance which 

 must have effectually ensured the passage of the ovum into the oviduct. 



In two of the specimens, the left ovary presented two empty ovisacs, or corpora 

 lutea (Plate XXV. fig. 2. h.), corresponding with the number of ova found in the 

 uterus. In the third specimen, the left ovary presented two ovisacs still uncicatrized, 

 but only one ovum was contained in the uterus. In a fourth specimen, three similar 

 ovisacs were present, but the ova had been removed from the uterine cavity. 



The discharged ovisacs were of an elongated flask-shaped form, about three lines 



* Natural history owes much to this gentleman ; he discovered what had so long been a desideratum in 

 science, the animal of the Pearly Nautilus, and first transmitted to this country the impregnated uterus of the 

 Kangaroo ; and now his indefatigable exertions have materially contributed to elucidate the still more obscure 

 subject of the generation of the Edentate Marsupiata. 



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