458 



EFFECT OF HEAT 



[Ch. xvm 



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 

 literatm-e vfhioh 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 larvse reared 

 at 23° to 27° C. passed 

 the fourth molt in 

 about 10 days, or 3 

 days earlier than lar- 

 \sd reared at 19° C. 



(HERKICK,'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.") 



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 



24°23'22fSl°29'U=18'17'l6'l6°14'l3°12=ll'l0"9' &' 7° 6= 6° 1° 3° 2° 



Fig. 131. — Curves showing the relation between the num- 

 ber ol days (ordinates, Indicated at left) required lor 

 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.) 



