The material on which this paper is based was collected partly by Prof. J. P. Hill and partly by myself. The uterine swellings with their contained embryos were fixed entire, either in Bouin’s picro-formol-acetic mixture or in corrosive-sublimate-formol-acetic. The former gave good general fixation and penetrated well, even into the larger specimens. Tissues fixed in it were considerably easier to cut than those preserved in corrosive formol. In order to preserve the fœtal membranes as far as possible intact, it was desirable not to open the uterine swellings, except in the latest stages, where it was, of course, necessary; hence a considerable time was required for the penetration with paraffin. It is very doubtful if a vacuum embedding bath is desirable for objects of this nature. Membranes may be ruptured unless the change in pressure is very gradual, hence I found it preferable to reduce the possibility of air bubbles forming in the interior of the uterus by employing air-free fixing solutions, followed by air-free alcohols of increasing strength. Clearing was carried out in cedar-wood oil and the tissues transferred direct to paraffin. Little trouble was experienced with air in the interior of the uteri, and this method of employing air-free solutions is well worth the slight extra trouble. If tissues are transferred from aqueous solutions into alcohol the air contained in the water is liberated in the tissues and cannot later be easily removed, since the stronger the alcohol the less air it is capable of dissolving.