The Orientation of the Frog's Egg

Abstract

The classical experiments of Pflüger on the segmenting frog's egg, and the important conclusions drawn by Roux from a study of the same egg, have made it very desirable to have an accurate knowledge of the relation existing between the early segmenting egg and the position of the embryo with respect to the egg. Our work in relation to the orientation of the embryo has covered the ground somewhat more extensively than that of any previous author, since we have made use of the methods employed by all of them. Our results will be considered under three headings: 1st. Normal development and location of blastopore. 2nd. Results obtained by injury to definite portions of the early embryo. 3rd. Results obtained from embryos whose development had been modified by artificial means. A word of personal explanation ought to be added. The senior author is responsible for Sections I, II, IV, and V of the present paper. The work recorded in these was done in the spring of 1893. Section II is the record of the results obtained by Umè Tsuda while a student in the Biological Laboratory of Bryn Mawr College. This work was done during the winter of 1891-2 j the account written in the spring of 1892. Only very slight alterations have been made in this portion preparatory to publication.

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