422 EDWIN G. CONKLIN. 



EXPLANATION OF PLATE III. 



FIGS. 13-18 were subjected to temperature so high (37), or for so long a period 

 (35 for four hours) that further cell division was stopped in almost all cases, 

 though the protoplasm remained transparent and apparently alive. 



FIG. 13. No. 1171(2). 37, ^ hr. during first cleavage; room temperature 

 (ca. 25) 15 hrs. Astral areas are large and distinct; chromosomes are widely 

 scattered or clumped in two principal masses outside the astral areas and at the 

 surface of the egg; chromosomes do not become vesicular. 



FIG. 14. Same slide as preceding;. subjected to heat during second cleavage, 

 and showing results similar to preceding. 



FIG. 15. No. 960. Ca. 35, 4 hrs., during resting 2-cell stage. The plasma 

 is much contracted and vacuolated and the chromatin of the nuclei is in the form 

 of hollow spheres, which look like chromosomal vesicles. 



FIG. 16. Same slide as preceding; heated during second cleavage mitosis; 

 plasma shrunken and chromosomes in the form of vesicles. 



FIG. 17. No. 1171(2). 37, | hr., during fourth cleavage; room temperature 

 (ca. 25) 15 hrs. Chromosomes in the macromeres are clumped together at the 

 surface of the egg, and are outside the plasma areas. There is a triaster in one 

 of the micromeres, while the others appear normal. 



FIG. 1 8. Same slide as preceding; 24-cell stage. All centrospheres instead of 

 being at the surface, as in normal eggs, are at the deeper ends of the cells next to 

 the spacious segmentation cavity. 



