SECT. 2] 



AND WEIGHT 



505 



stage at 10°. Thus the velocity of the process is more than tripled 

 by a rise of 10° in the temperature, as would ordinarily be expected 

 in the case of a chemical reaction. Judging from Hertwig's curves 

 alone, one should theoretically be able to increase the speed of the 

 growth to infinity by heating the system up, but this of course is 

 not the case, and Fig. 77 taken from Faure-Fremiet's work on 

 Sabellaria eggs shows how, after a certain temperature is reached, 

 the growth-rate may get slower again, owing to the destructive effects 

 of excessive heat on protoplasm. The subject was thoroughly gone 

 into, apparently at Abegg's suggestion, by Peter in 1905, who made 

 many measurements of the development of echinoderm eggs and 

 calculated out the temperature coefficients of Hertwig's results more 

 correctly. His results were as follows: 



Table 69. 



2-cell stage ... 



4-cell stage ... 



8-cell stage ... 

 i6-cell stage ... 

 32-cell stage ... 

 Blastula 

 First mesoderm 

 First spicule ... 

 Full spicules ... 

 Prisma 



Young pluteus 

 Old pluteus ... 



From these figures Peter concluded that the average tempera- 

 ture coefficients of the three embryos were not very different, 

 i.e. Sphaerechinus 2-15, Echinus 2-13, and Rana 2-86. He regarded 

 the similarity between the values for the echinoderms as significant. 

 He observed also that Q,io ^^^ i^ot quite a constant : thus between 

 2'5 and 14-5° it was 3-28 (average) and between 14 and 24° it 

 was 2-26; or in other words that the development at low tem- 

 peratures was rather slower than it ought to have been if the 

 same temperature coefficient held for all temperatures. Next Peter 

 noted that Q_^q was not the same for each stage of development, 

 for, on the whole, the average coefficient for the cleavage pro- 

 cesses was higher than that for the later events. This rule, however, 



