No. 2.] EARLY DEVELOPMENT OF AMBLYSTOMA. 347 



shrinkage of the eggs, often producing artificial delaminations 

 and cavities, it was found necessary to discard the latter. 

 Serial sections by the method which I have described in an- 

 other place ('92) have been used for the most part. A method 

 which I found very instructive was to imbed several eggs 

 without reference to planes. This obviously necessitated recon- 

 structions. 



In reconstruction the wax plate method gave most satisfac- 

 tory results. I have also profited by camera lucida drawings 

 on panes of glass ; the outlines of the various structures being 

 drawn in water colors. By combining these, a graphic repre- 

 sentation of the embryo is obtained. Projections on ruled 

 paper have also assisted in gaining an idea of the structures. 



In the present paper I shall omit entirely the discussion of 

 the phenomena of maturation and fertilization, since these sub- 

 jects have been so thoroughly studied by Jordan ('93) in the 

 Newt and Fick ('93) in the Axolotl. 



2. The Unsegmented Ovum. 



The fertilized ovum of Amblystoma is nearly spherical, being 

 slightly flattened at the pigmented pole and measuring about 

 2 mm. in diameter. The upper portion presents a deep brown 

 color (PI. XVIII, Fig. i), which in a zone just above the 

 equator changes quite abruptly to a lighter shade, and fades 

 away into a faint yellow at the opposite pole. A marked differ- 

 ence in the density of pigment on the opposite side of the 

 upper hemisphere is often noticeable. While this difference 

 is by no means constant, I believe it of sufficient importance 

 to be kept in mind with reference to the orientation of the 

 embryo. 



If the Q:gg be examined a few hours after deposit it presents 

 the appearance shown in Fig. 2. There is a very conspicuous 

 saucer-shaped depression surrounded by a zone in which the 

 pigment is less dense than in other portions ; to this area 

 various names have been applied, as, "Keimpunkt," "fovea 

 germinativa," "trow vitellin," "light spot," etc. Slight mag- 

 nification reveals at its center a small pit in which the first 

 polar globule lies. 



