' ' ' ( " : 359 



The eggS arc not iii I IP . .1 ma I uril \ a t t he I ime of oviposit ion , 



as at :..\ 1. we have fmm <> In i S day- U the length nf flu- Tage." 



\ regards the threshold of development, Sanderson I mi in I thai eggs 

 of tlu* nif;il worm, Tent-brio ;;/)//// faile 1 to hatch at ; 01 tO C, \>\i\ 

 hatched a! . 



The time from the deposition of the c<^s to hatching of the chinch 



buir is variable. brin.u longer if temperature i> low, or >horter if hi^h. 



Thus lirst brood e<^ r s (June) with an average mean temperature of 73 F. 



i in 17.3 days; and second brood eggs (August) at 76.58 F. in 11.45 



tin- average for both broods being 14.4 days (Headier and 



McCollochL 



Larval Development. The discussion already given of growth and 

 development in relation to temperature applies of course to the larval 

 Mau r c as well as to all other stages of development. 



Larvae of the cotton boll weevil in squares developed in 7 days at 

 an average mean temperature of 75 F.; the total of effective tem- 

 peratures being 280 degrees F. (Hunter and Hinds.) 



The bollworm, or corn ear worm, developed in 21 days at an average 

 mean temperature of 77 F.; the total of effective temperatures being 

 617 degrees F. (Quaintance and Brues.) 



In these experiments it was assumed, as was formerly customary, 

 that only temperatures above 43 F. were effective for growth; this is 

 known to be a mistake. A small percentage of bollworms survive 

 a temperature of 34 F.; but larvae subjected to temperatures somewhat 

 below freezing for one to two days are killed outright. 



A constant temperature of 90 F. prevents the development of the 

 plant louse, Aphis avence; the optimum temperature for the production 

 of the wingless agamic forms being about 65 F. (H. E. Ewing.) 



Warmth and dryness are favorable to the development of species 

 of "thrips" (Thysanoptera) and of the "red spider," a well known 

 mite that injures plants, especially in greenhouses. 



Molting. In the walking-stick, Diapheromera femorata, a low tem- 

 perature lengthens, while a high temperature shortens, on an average, 

 the interval between molts. A low temperature has a tendency to 

 decrease the number of molts, while a high temperature increases the 

 number. (H. H. P. and H. C. Severin.) 



Pupal Development. Krogh found that the extremely simple 

 relation (already described) between temperature and the velocity of 

 embryonic development held good also for the changes taking place 

 during the pupal life of the meal worm, Tencbrio molitor. He - 



