MAMMALIA. 



reproduction is concerned, from all the Mammiferous inhabitants of 

 the Old World, that they might even be regarded as forming 

 quite a distinct and separate group in the animal creation, serv- 

 ing to accomplish another step in that grand transition by which 

 the physiologist is conducted from the oviparous to the placental 

 Vertebrata. 



The Marsupialia are, strictly speakingj ovo-viviparous, that is 

 to say, the uterine ovum never forms any vascular connection with 

 the maternal system, but after a very brief intra-uterine gestation the 

 embryo is expelled in a very rudimentary and imperfect condition, 

 even its extremities being as yet but partially developed ; and in 

 this helpless state the fetus is conveyed from the uterus into a pouch 

 or marsupium,) formed by the integument of the abdomen, there 

 to be nourished by milk sucked from the mammary glands, until 

 it arrives at such a state of maturity as enables it to assume an 

 independent existence. 



We may naturally expect, therefore, that, with habits so remark- 

 able, the structure of the generative apparatus, both in the male 

 and female Marsupial, will offer important peculiarities, and these 

 accordingly first present themselves for description. 



(837.) We select the Kangaroo as an example of the entire 

 group ; beginning, as we have hitherto done, with the organization 

 of the male organs of generation. 



The first circumstance that strikes the attention of the anatomist 

 in a male Marsupial is the extraordinary position of the testes, 

 which, instead of being situated behind the penis, as in most pla- 

 cental Mammals, are placed in front of that organ in a kind of 

 scrotum that occupies the same place as the pouch of the female, 

 and is in like manner supported by two marsupial bones derived 

 from the pubes, around which the cremaster muscle winds in such 

 a manner as to enable it powerfully to compress the testicles 

 during the congress of the sexes. The vasa deferentia derived 

 from the testes open into the commencement of the urethra, which 

 now, for the first time, forms a complete canal leading from the 

 bladder to the extremity of the penis. The auxiliary glands that 

 pour additional secretions into the urethra are of great size, and 

 more numerous than those met with in the human subject. In 

 the first place, the commencement of the urethral tube is em- 

 braced by a bulky and conical prostate^ to which succeed three 

 pairs of large secreting organs (Cowper's glands), each enveloped 

 in a musculo-membranous sheath, apparently intended to compress 



