Experiments on the Early Development of the Amphibian Embryo etc. 619 



solution developed without any loss, being used up gradually in the 

 preservation of material at regular intervals. Those in the 0.4 % 

 solution for some reason died before escaping from the egg membranes. 

 From a careful study of the eggs developed in the 0.6 "/o solution 

 by means of surface views taken while the eggs were still alive, 

 and by sections of the preserved material we can trace the following 



Development of the Embryo. Segmentation. 

 Segmentation is considerably delayed and resembles very closely 

 that of eggs subjected to a low temperature, as noted by Hertwig 

 (23). Sections of eggs taken during segmentation reveal the fact 

 that the nucleus divides some little time before the protoplasm, and 

 cells may often be found in which the nucleus has divided while 

 the protoplasm still remains undivided. The same is true of cells 

 at or near the centers of activity in all subsequent development. As 

 a result karyokinetic figures are of frequent occurrence. Indeed I 

 would venture to suggest this method of development in a 0.6% salt 

 solution as a useful means in karyokinetic investigation. We see 

 clearly, therefore, that the egg is affected in its different parts un- 

 equally by the salt solution, the vegetative half being hindered more 

 than the animal half as Hertwig notes. There is also a correspond- 

 ing inequality in each cell, the protoplasm being affected more than 

 the nucleus, as Loeb has well shown (33). 



Segmentation Cavity. 

 At the end of the third day the yolk cells are still very large. 

 In section they appear as spherical masses made up of coarse 

 granules and lying loosely in the segmentation cavity, many of them 

 entirely free (Fig. 11). Consequently the floor of the cavity is not 

 clearly defined as in the normal egg, but it is very irregular, and 

 the large cells forming the yolk plug fuse toward the surface into 

 a coarsely granular homogeneous mass. This irregularity of the yolk 

 cells is found in subsequent stages, and makes it difficult, sometimes, 

 to determine the exact arrangement of different parts. There are no 

 traces of any ectoderm covering this yolk plug, the outer cells being- 

 like the inner ones save for the presence of pigment (Figs. 12 and 13 i. 



Gastrulation. 



Eycleshymer (14) states that »invagination always begins nearer 

 the equator than the vegetative pole« in normal eggs, and that it 



