Among the specimens collected by the Scottish National Antarctic Expedition and brought back to this country was a series of the embryos of penguins of various species, collected at different stages of development by Mr R. N. Rudmose Brown and Dr J. H. Harvey Pirie. These embryos were, for the greater part, of the species Gentoo (Pygoscelis papua, Forst.), the remainder of the species Adelia (Pygoscelis adeliæ, Hombr. and Jacq.). Two Emperor penguins, which had been preserved for examination by the injection of the blood-vessels, were also brought home. Through the kindness of Dr W. S. Bruce these specimens were entrusted to one of us (D. W.) for examination and report, but as the work involved in this proved to be very extensive, Dr A. Campbell Geddes was asked to undertake a share in it, and this he agreed to do.This report contains the results of the combined investigations.