VIII. Researches on the impregnation of the ovum in the amphibia; and on the early stages of development of the embryo. ( third series.)

In a note dated April 18th, 1853, which was added to my last paper on the “ Impregnation of the Ovum'',” whilst it was printing, I recorded the fact that, “ through the adoption of a different mode of examination” from that which I had previously employed, I had seen the spermatozoon pass through the gelatinous covering and the vitelline membrane of the egg into the vitelline chamber and the yelk.