10 INTRODUCTION. 



part of the skeleton of this animal ; hut even with these materials 

 I found I could not produce an accurate re])resentation of it in 

 the living state. Although I do not inflict upon my readers 

 the characters and distinctions of genera, I must not pass over 

 uunoticed the principal features which distinguish the Mursu- 

 piata from the Placental Mammalia. In the first place, the 

 former are considered to be much less highly organized than the 

 latter : according to Professor Owen, the brain is deficient in 

 both the cor])uscallosum and the septum lucidmn ; the cerebrum 

 is small in proportion to the animal, contracted in front, and its 

 surface is smooth, or presents but few convolutions ; the cere- 

 bellum is entirely exposed, and has a vermiform process large in 

 proportion to the lateral lobes; the olfactory lobes are large. 

 Two venae cavae enter the heart; "the right auricle has no trace 

 of a fossa ovalis." In point of fact, the main characteristic of 

 the ]\Iarsuj)ials, as distinguished from the Placentals, is that 

 much of the embryotic life in the former is carried on in what 

 may be called a sort of external uterus. 



On my return from Australia, the venerable GeofFroy St.- 

 Ililaire put the following question to me, " Does the Ornitho- 

 rhynchus lay eggs ? " and when I answered in the negative, that 

 fine old gentleman and eminent naturalist appeared somewhat 

 disconcerted. Now, this oviparous notion was nearly in accord- 

 ance with the true state of things — somewhat akin to what is 

 actually the case; and I consider the most striking ])eculiarity of 

 this singular annual, and indeed of all the Marsupiata, to be 

 the imperfectly formed state in which their young are born. 

 The Kangaroo at its birth is not larger than a baby's little 

 finger, which it is not very unlike in shape : in this extremely 

 helpless state, the mother, by some means at present urdcnown, 

 places this vermiform object to one of the ni|)ples within her 

 pouch or marsupium ; by some equally unknown process, the 

 little creature becomes attached by its imperfectly formed mouth 

 to the nipple, and there remains dangling for days, and even 

 weeks, during which it gradually assumes the likeness and struc- 



