§1] 



UPON THE RATE OF GROWTH 



459 



TABLE LII 



Showing for Three Species op Tish the Interval, in Days, elapsing 

 BETWEEN Fertilization and Hatching, at Various Temperatures 



Rauber ('83) states that eggs of minnows and salmon, -which develop 

 during the winter season, will not grow at much above 12°-15°, but will do so 

 at 0°. On the contrary, eggs which normally develop during the summer 

 grow better at the higher temperatures. 



Amphibia — The European Rana is said not to develop at 0° (Schultzb, 

 '94), and the same is true of the Amblystoma tigrinum of the United States. 

 (LiLLiE and Knowlton, '98). The time required to attain a definite stage, 

 at which the chorda is well developed and head and tail are sharply marked, 

 is for Rana temporaria: at 15°, 6 days; at 33°, 1 day (Hertwig, '96). If 

 brought gradually to it tadpoles may develop at 37°, or even for a few hours 

 at 40°, but they do not thrive long at this temperature. The great effects of 

 temperature on rate of development of the frog are illustrated by Fig. 132. 



Birds develop only at a high temperature and within narrow limits. 

 The normal for the chick is 38°, the minimum is 25°, the maximum near 

 42° (Rauber, '84). FsSre ('94) has determ.ined the rate of development of 

 the chick's egg incubated at different temperatures. One lot at an abnor- 

 mal temperature and a second at 38° were reared synchronously; after a 

 time the eggs were opened and the average stage of development (in hours 

 of a standard series) determined. The following numbers express the ratio 

 of the stage of development at the abnormal temperature to the stage at the 

 normal temperature of 38° : — 



Temperature .... 34° 35° 

 Index of Development 0.65 0.80 



In summarizing these scattered observations on growing animals we may 

 exhibit in one table their critical temperatures. 



* The stage at 37° is taken from too few observations to be trustworthy. The 

 stages at 35° and 36° are irregular, doubtless because of too few observations. 

 As we go beyond 41° the ratio must decline again with great suddenness to 0. 



