334 MR. OWEN ON THE GENERATION OF THE MARSUPIAL ANIMALS. 



limited in the mammiferous class to this division, in which alone, from the peculiarly 

 brief period of uterine gestation, and the consequent non-enlargement of the abdomen, 

 their presence might be expected. But these bones serve important purposes in 

 relation to the generative economy of the Marsupiata. In the female they assist in 

 producing a compression of the mammary gland necessary for the alimentation of a 

 peculiarly feeble offspring, and they defend the abdominal viscera from the pressure 

 of the young as these increase in size during their mammary or marsupial existence, 

 and still more when they afterwards return to the pouch for temporary shelter. 

 In the males, with the exception of the edentate genera, the marsupial bones, from 

 their relation to the cremaster muscles, which wind round them like pulleys, assist in 

 the compression and retraction of the testes during coition ; a process which, from the 

 peculiar position of the scrotum, has been supposed to differ from that of other qua- 

 drupeds. A recent opportunity, however, of observing the coitus of the Kangaroo at 

 the Zoological Gardens, proves that there is no difference as to position, which is the 

 same as in the Dog, but that it is chiefly remarkable for the frequent repetition of the 

 act during a long-continued embrace. The peculiar length and tortuosity of the 

 double vagina, for which the bifurcated glans of the male organ is adapted, may 

 render necessary so efficient a process ; and as the testes are then retracted entirely 

 out of sight, it would seem that the marsupial bones have the same relation in the 

 male to their secretion as they have in the female to that of the mammary glands. 



The minute size of the young of the American Opossum when found in the marsu- 

 pium, their pendulous attachment to the nipples, and perhaps the mode in which the 

 latter were developed, gave rise among the earlier observers to a supposition that they 

 were originally formed from those parts, and the gemmi parous theory, which has sub- 

 sequently often been revived, appears to have been prevalent at the time when Tyson 

 first devoted his attention to the subject. 



The discovery of the uterus of the Opossum, recorded by Tyson in the twentieth 

 volume of the Philosophical Transactions (p. 139.), was the first step towards a cor- 

 rect explanation of the generative economy of the Marsupiata. That learned and 

 accurate anatomist offers a true conjecture as to the parts of their complex uterine 

 apparatus in which the processes of gestation are carried on, which he denominates 

 the comua uteri, and is the first who distinguishes the true vaginae from the " com- 

 mon passage, or canalis,'' subsequently termed the urethro-seocual canal. 



The subject of marsupial generation has ever since been regarded as one of peculiar 

 physiological interest, and the labours of Hunter*, Home-J-, Geoffroy St. HilaireJ, 



* Zoological Appendix to White's New South Wales, p. 272. 



t Philosophical Transactions, vol. Ixxxv. (1795) ; Lectures on Comparative Anatomy, iii. 



X 1) Journal Compl^mentaire du Dictionnaire des Sciences MMicales, torn. iii. p. 193. (1819.) " Si lesani- 

 maux k bourse naissent aux t^tines de leur mfere ?" 2) Systeme sexuel des Animaux a bourse, Mem. du Mus, 

 torn. ix. p. 193, (1822.) 3) Anatomie Philosophique, torn. ii. pp. 354, 397. 4) Art. Marsupiaux, Diet, des 

 Sciences Nat. torn. xxix. (1823.^ 



