458 



EFFECT OF HEAT 



[Cn. XVIII 



stantly diminishing increment to the optimum, and then a 



rapid decline to the maximum. 



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 

 A pus 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. 

 (HEiiuiCK,'96,p. 190). 

 Jnsecta. 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.") 



Degrees 25 20 15 10 



Days 50 55 60 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 



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.) 



