part of the skeleton of this animal; but even with these materials I found I could not produce an accurate representation 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 unnoticed the principal features which distinguish the Marsupiata 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 corpus callosum and the septum lucidum; the cerebrum is small in proportion to the animal, contracted in front, and its surface is smooth, or presents but few convolutions; the cerebellum is entirely exposed, and has a vermiform process large in proportion to the lateral lobes; the olfactory lobes are large. Two venæ cavæ enter the heart; "the right auricle has no trace of a fossa ovalis." In point of fact, the main characteristic of the Marsupials, 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. Hilaire put the following question to me, "Does the Ornithorhynchus 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 accordance with the true state of things—somewhat akin to what is actually the case; and I consider the most striking peculiarity of this singular animal, 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 unknown, places this vermiform object to one of the nipples 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-
