XIX. Researches in embryology.—Second series

Abstract

In a former communication I described the mammiferous ovum in its several pe­riods of formation. The present paper is intended to trace it through the early stages of development. What is known, or supposed to be known, of the evolution of the mammiferous ovum in its early stages, mainly rests on observations made, not in Mammals, but in Birds. Direct observations have been so few and so isolated, that between the time when the coitus takes place, and that of the incipient appearance of the vertebræ, there exists a dark period of which very little is really known. This hiatus it is one of the objects of the present paper to assist in filling up.