EXPERIMENTS WITH FROG'S EGGS. 8l 



in turn is the outcome of the pressure relations of the cells on 

 each other. 



EFFECTS OF COLD ON THE EARLY DEVELOPMENT. ' 



In a preceding paper 1 I have described some abnormal embryos 

 of the frog that were produced as the result of cold. The early 

 segmentation stages of these eggs were not preserved, but I can 

 now make good this deficiency by means of a series of young 

 stages kept under similar condition (i to 2 C), that have been 

 put up for me by Dr. N. M. Stevens. 



The most obvious effect of the cold is of course to delay the 

 development. The secondary effects involve (i) greater injury 

 to the yolk cells than to those of the upper hemisphere, (2) 

 effects on the formation of the segmentation cavity, and (3) in 

 some cases the retention of the small cells at the upper hemisphere. 

 How far this latter change may be directly connected with the 

 injury to the lower cells, so that they fail to draw inwards, is a 

 point difficult to determine, but if the cold is responsible for the 

 failure of these cells to draw inwards, the retention of the small 

 cells at the upper pole may directly result. 



The details of the development of these eggs, left on the ice 

 for eleven days, are as follows (the eggs were put on the ice April 

 9, at 10 a. m.) : 



April 9, i p. m. Some eggs still in the four-cell stage, others 

 going into eight cells. 



April 9, 6 p. m. Eight-cell stage. Small segmentation cavity 

 present. 



April 10, 9 a. m. Some eggs going into the twelve-cell stage. 

 The segmentation cavity is well developed (Fig. 18). 



April 10, 5 p. m. Sixteen-cell stage. The segmentation 

 cavity extends far down into the yolk. 



April ii, 9 a. m. Another cell division has taken place. A 

 large segmention cavity has developed (Fig. 19). 



April 11, 8 p. m. Immigration of cells at the top of the egg 

 taking place. Segmentation cavity better developed on one side 

 than on the other. 



1 Roitx's Archiv, XIX., 1905. 



