280 



gestive organs, being evidently a provision for their early or prema- 

 ture exercise. 



From the close resemblance in the structures of the ovary and Fal- 

 lopian tubes of the kanguroo with those of ordinary mammalia, and 

 from the circumstance of the young being nourished, after birth, by a 

 secretion from mammary glands, the author concludes that the ovu- 

 lum in the former animal quits the ovisac in a condition correspond- 

 ing to that in the latter class, and increases in a similar manner as it 

 descends to the uterus. But as there is no formation of a placenta, 

 it remains to be determined how the aeration of the foetal blood is 

 effected : this, however, probably takes place through the chorion, 

 although this membrane is not vascular, to an extent sufficient for the 

 purposes of the vital functions of a foetus so imperfect, and whose 

 uterine existence is of such short duration, as they are in this animal. 

 Reasons are given, which render it probable that in the Marsupiata an 

 allantois and umbilical arteries are developed at a later period of 

 gestation, corresponding in this respect to the foetal condition of the 

 Batrachian reptiles, and corroborating the views entertained by the 

 author, that the former family are essentially ovo-viviparous. 



The author next proceeds to investigate the structure and condition 

 of the mammary foetus in the Marsupiata, or that stage of its exist- 

 ence when it is retained in the marsupial pouch, and derives its suste- 

 nance from the imbibition of milk from the mammary glands. He 

 relates the observations which he has lately made on the foetus of a 

 kanguroo in the Menagerie of the Zoological Society. He ascertained 

 that the period of uterine gestation in the animal is thirty- nine days, 

 and examined the foetus a few hours after it had fixed itself to the 

 nipple in the abdominal pouch, and when it was not much above an 

 inch in length, and resembled an earth-worm, both in the colour and 

 the semi-transparency of its integument. Four days afterwards, he 

 detached it from the nipple, and observed that although it moved its 

 limbs freely, it was unable to regain its former situation. The pa- 

 rent endeavoured to replace it by introducing its head into the pouch, 

 which it held open with its fore paws; but these efforts were in- 

 effectual, and the next day the foetus had disappeared, having, pro- 

 bably, been destroyed by the mother. 



The last section of the paper is occupied by an inquiry into the 

 structure and analogies of the female generative organs of the Mar- 

 supiata. These are traced throughout the successive orders of mam- 

 malia, to their connexions with various tribes of birds and reptiles, 

 and is concluded by a disquisition on the final purposes of marsupial 

 generation, and its relations to the other modes by which the con- 

 tinuance of the race is accomplished, in the more elevated orders of 

 animals, and which appear to have reference to the greater expansion 

 and perfection of the brain, and the greater developement of the in- 

 tellectual faculties. 



A paper was then read, entitled, "On a new Law of Combustion." 

 By Charles J. B. Williams, M.D. Communicated by W. G. Maton, 

 M.D., F.R.S. 



