Ill] THE EFFECT OF TEMPERATURE 117 



Karl Peter*, experimenting chiefly on echinoderm eggs, and 

 also making use of Hertwig's experiments on young tadpoles, 

 gives the normal temperature coefficients for intervals of 10° C. 

 (commonly written Q^q) as follows. 



Sphaerechinus ... ... ... 2-15, 



Echinus 2-13, 



Rana 2-86. 



These values are not only concordant, but are evidently of the 

 same order of magnitude as the temperature-coefficient in ordinary 

 chemical reactions. Peter has also discovered the very interesting 

 fact that the temperature-coefficient alters with age, usually but 

 not always becoming smaller as age increases. 



Sphaerechinus ; Segmentation Q^" = 2-29, 



Later stages ,, 2-03. 



Echinus; Segmentation ,, 2*30, 



Later stages ,, 2-08. 



Rana; Segmentation ,, 2-23, 



Later stages ,, 3-34. 



Furthermore, the temperature coefficient varies with the 

 temperature, diminishing as the temperature rises, — a rule which 

 van't Hoff has shewn to hold in ordinary chemical operations. 

 Thus, in Rana the temperature coefficient at low temperatures 

 may be as high as 5-6 : which is just another way of saying that 

 at low temperatures development is exceptionally retarded. 



In certain fish, such as plaice and haddock, I and others have 

 found clear evidence that the ascending curve of growth is subject 

 to seasonal interruptions, the rate during the winter months 

 being always slower than in the months of summer : it is as though 

 we superimposed a periodic, annual, sine-curve upon the continuous 

 curve of growth. And further, as growth itself grows less and less 

 from year to year, so will the difference between the winter and 

 the summer rate also grow less and less. The fluctuation in rate 



* Der Grad der Beschleunigung tierischer Entwickelung durch erhcihte 

 Temperatur, A. f. Entiv. Mech. xx, p. 130, 1905. More recently, Bialaszewicz 

 has determined the coefficient for the rate of segmentation in Rana as being 

 2-4 per 10° C. 



