Abstract
Stnce my first attem pt to work out the Mammalian type of skull, the greater part of my time has been spent upon Cold-blooded Vertebrata—Fishes, Amphibia, and Reptiles. But between the early part of 1873, when my paper on the skull of the Pig was presented to the Royal Society, to the beginning of 1882, when I was able to take up this Class . once more, no time or chance was lost as far as materials for work go ; during those nine years a very large collection of embryos and of early young of the various types of Mammalia was made.