No. 4.] THE DEVELOPMENT OF ANIMALS. 185 



dark pole would probably show a maximum above the optimum, 

 and similarly for the white ; but we are not able to prove this. 

 It is also conceivable that the coincidence of optimum and 

 maximum is due to the complexity of the processes involved, the 

 temperature range possibly differing for the different factors 

 concerned, such as cleavage, invagination, differentiation, etc. 



Let x equal the decrease in time for each degree increase in 

 .temperature; the next table shows its value for Amblystoma 

 and the following one for the frog. 



4 to 8 C., x 19.5 hours. 



8 " 13 C., x - 22.8 " 

 13 " 1 8 C., x 7.2 " 

 18 " 22 C., x = 5 



TABLE V. Amblystoma. 



4 to 8.75 C., x = 58.7 hours. 



8.75 " 12.12 C., x 23 " 

 12.12 " 1 6 C., x 16.5 " 

 16 " 22 C., x 5.4 " 



22 " 26 C., X - 1-5 " 



TABLE VI. Frog. 



The same law holds as for Planaria : between the minimum 

 and the optimum the rate of decrease in time of development 

 diminishes with each degree rise in temperature. 



Below 14 eggs of Amblystoma develop more rapidly than 

 those of the frog, and above less rapidly ; sec curves (Fig. 2). 

 The eggs of the frog also develop above the maximum for 

 Amblystoma. This is undoubtedly an inherited effect of the 

 different temperatures to which the eggs are normally exposed, 

 as noted before. 



b. Snbminimal and Snpramaximal Temperatures. - - Submin- 

 imal temperatures have the same effect on the cleavage of the 

 eggs of both forms. At o C. cleavage is entirely inhibited. 

 If the eggs of Amblystoma were put in a vessel containing ice 

 and the vessel placed on ice in the refrigerator, cleavage was 

 inhibited entirely or to a great extent in the white hemisphere, 

 though it went on slowly and fairly normally in the dark hemi- 

 sphere ; death occurred before gastrulation, the temperature 

 being about i C. The same effect was produced in eggs of the 



