Royal Society. 4. r >9 



The three omphalo-mesenteric, or vitelline vessels, were traced, from 

 the umbilical cord into the abdomen, where they terminated in the 

 usual manner; namely, the veins in the vena portae, and the artery 

 in the aorta. Hence it was apparent that the membrane on which 

 they ramified, corresponded to the vascular layer of the germinal mem- 

 brane, which, in oviparous animals, spreads over the yelk, or to the 

 umbilical vessel of the embryos of ordinary mammalia. The ventri- 

 cles of the heart were completely joined together, and bore the same 

 proportions to each other as in the adult ; a perfection of structure 

 which is not observed in the embryos of ordinary mammalia at a cor- 

 responding period of developement. The lungs were equal in size to 

 the heart, and were of a spongy texture, and full of red blood; their 

 precocious developement, compared with that of the abdominal or di- 

 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 kangaroo 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 

 kangaroo 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- 



• For an account of there observations, -ee our present volume, p. 304, 



in the number for April.— Edit. 



