96 



DEVELOPMENT OF THE FROG'S EGG 



[Cii. X 



hardened) 1 measured in its longer diameter, parallel to the 

 two plates, 1.83 mm., while the shorter diameter, at right angles 

 to the plates, was 1.2 mm. The two axes, therefore, stand in 

 the relation of 2 : 8. These figures apply to eggs compressed 

 in the direction of the egg-axis, from above downward. When 

 the egg is compressed from side to side it will withstand 

 more pressure. With a distance of 1.37 mm. between the two 

 parallel plates, an egg compressed laterally measured in its 

 longer diameter 1.96 mm., while its shorter diameter, from 

 plate to plate, measured 0.91 mm. The two axes therefore 

 bear to each other the ratio of 1:2. The experiments may 

 be described in detail under the following categories. 



1) Eggs compressed in the direction of the primary axis (Fig. 30, 

 A). The eggs taken from the uterus were placed on a dry plate 



B 



Fig. 30. — Diagram showing three positions of eggs under compression. 



of glass, so that the white pole was exactly downward, i.e. the 

 egg-axis was vertical. Another glass plate was then placed 

 over the eggs and brought down into contact with two sup- 

 porting rods, so that the two glass plates were 1.4 mm. apart, 

 and the eggs correspondingly compressed. The eggs were then 

 fertilized and the whole apparatus put into a dish of water. 

 The primary axis of each egg was kept always vertical. When 

 the first furrow comes in, it is vertical, i.e. at right angles to 

 the glass plates, and passes from the black to the white pole 

 (Fig. 31, A), dividing the egg into two symmetrical halves. The 

 second furrows come in at right angles to the first, and are also 



1 The eggs contracted very little during the process of hardening. 



