458 



EFFECT OF HEAT 



[Cn. XVIII 



stantly diminishing increment to the optimum, and then a 

 rapid decline to the maximum. 



>_^^ T _^_ T ^_ __ T _^-^-^l. r _^_^^ T _ r-~r ,^- Although many ob- 



servations upon the 

 effect of heat on the 

 growth of animals have 

 been made, they have 

 been mostly fragmen- 

 tary. I have gathered 

 certain cases from the 

 literature which it may 

 not be useless to repro- 

 duce here. 



Echinodermata. 

 According to VERNON 

 ('95) the optimum for 

 the development of 

 Echinoid larvae is 7 

 22. 



Crustacea. Nauplii 

 of Branchipus and 

 Apus hatch out at a 

 temperature of 30 in 

 less than 24 hours, 

 whereas at 16-20 they 

 require some weeks 

 (SEMPER, '81, p. 129). 

 Lobster larvae reared 

 at 23 to 27 C. passed 

 the fourth molt in 

 about 10 days, or 3 

 days earlier than lar- 

 vae reared at 19 C. 



(HERRICK,'96,p.l90). 



Insecta. The mi- 

 gratory locust is as- 

 serted to require at different temperatures the following times for hatching. 

 The figures are suspiciously regular. (From CUENOT, '94, p. 18, after 

 " CLEVELAND.") 



TE UPERATURE 



24 3 23 D 2221 20 3 19 3 18'17 3 16 D 15 3 JWPl3'12 D ll10 J 9 J 8 J 7 6 D 5" 4 3 s 2 1 



FIG. 131. Curves showing the relation between the num- 

 ber of days (ordinates, indicated at left) required for 

 the frog tadpole to reach a certain definite stage, and 

 the temperature to which it is subjected during devel- 

 opment. Stage I is that of a gastrula whose blastopore 

 is just closing; II, edges of medullary plate rising; 

 III, medullary tube completely closed ; IV, tail evi- 

 dent, but gills not formed; V, embryo 5 mm. long; 

 VI, embryo 7.5 mm. long; VII, 9 mm. long; VIII, 11 

 mm. long; IX, 11.5 mm. long. (From HERTWIG, '98.) 



Degrees 

 Days . 



25 



50 



20 

 55 



15 



60 



10 

 65 



Fishes. Many experiments have been made with these animals for com- 

 mercial reasons, as it is sometimes desirable to retard growth during trans- 

 portation or to delay hatching until the season of the natural enemies shall 

 have been passed. Some of the results are summarized in 



