EARLY DEVELOPMENT IN THE FROG. 



323 



e.g., in w/io,ooo HgCl 2 , are accelerated in development for a 

 short time, while gastrulating eggs die within a few hours (four 

 to six) in m/2, 000,000 HgCl 2 , without having developed farther 

 after being placed in the solution. The same relation holds for 

 other agents. Eggs from different females may differ consider- 



D 



FIG. 2. Diagrams of full grown ovarian eggs to show the position of the pedicle 

 in relation to the distribution of pigment. (See also Table I.) 



ably in their behavior when exposed to toxic agents; also eggs 

 from the same female may differ somewhat in susceptibility to 

 toxic agents but to a much less extent than in the former case. 

 Some difficulty is experienced in watching the progress of dis- 

 integration in early stages, especially in concentrations that kill 

 rapidly, on account of the spreading of the disintegrated proto- 

 plasm underneath the inner membrane, and thus obscuring the 

 rest of the process. However, the progress of disintegration, 

 wherever observed, is an orderly process and bears a definite 

 relation to the polar axis of the egg and to the axes of symmetry 

 of the embryo. 



(a) Unsegmented Eggs. The most satisfactory method found 



