This is essentially a critical summary of Dr. Loeb's work in artificial parthenogenesis. It gives a survey of the methods by which the unfertilized egg (of invertebrates and of vertebrates) can be caused to develop into an embryo, and the conclusions which can be drawn concerning the mechanism by which the spermatozoon produces this effect. Dr. Loeb believes that the fertilization of the egg by the spermatozoon involves two factors, one of the processes being akin to cytolysis, the other (designated the "corrective factor") causing a temporary depression of the oxidation in the egg. Both of these factors are probably independent of the material in the spermatozoon that serves as the vehicle of paternal heredity.
The problem of fertilization is intimately connected with many different problems of physiology and pathology, such as the natural death of the unfertilized egg and the prolongation of its life by fertilization, the fertilization of