EXPERIMENTS WITH CHRYSOMELID BEETLES. 2/ 



moderate intensity. Eggs that develop within an opaque mother, 

 or thai possess an opaque envelope, pass through their embryonic 

 stages in darkness; but there can be no doubt that the chorion 

 of the beetle's egg allows the light to penetrate, since, as 1 shall 

 -how in a later paper, sunlight has a decided influence upon 

 embryonic de\ elopment . 



In certain cases experiments have seemed to prove that dark- 

 lie-- dela\- the growth of the eggs or larvae, e. g., Yung (1878) 

 recorded not onl\ a retardation in the development of fro- larv.e, 

 but al-o ,i hi'Ji death rate. The same investigator noted a -liijit 

 irdation in tin- de\ el. .| .nieiit of the eggs of the snail, Lymmcd 

 ntlli'i. \\heil placed ill the dark. 



\"'-ni< .11 [895 . < m the i .1 her hand, found that echin< .derm lar\ ae 

 -niter \er\ little, it any, i haiue from the normal when reared in 



absolute darkness Loeb [896 also has brought forth evidence 



pr>\ in- that darkne-- doe- n,,i n-tard the embryonic de\ elopment 

 of the ti-h 1'nmlnlns, but <]< ; a decrease in the number of 



pigment cell- on the \ oik 3a< . 



In other cases, darkne-- does not hinder the growth of the 

 emluAo or lar\a. but tail- to -timnlate the hatching pn>< 

 I'r/ibrain i mid that the larva? of the praying manti-. 



Sphodromanti mled if the cocoon is placed in 



the dark. 



In di-cu--in^ experiment- ( . H. ^2 and (\H. 70, the normal rate 

 of de\elopmeiil and it- \ariations must be noted. Records of 



OVer 2, . >!<i an<l the clo-ely allied species C. 



ninltipntitttitd ij\e 5 da\- and to hours as the average- hatching 

 period rlegner, [9080). This period varies according to condi- 



lioii- of nioi-uire, teni|)eial m e and probabK" other external fac- 

 tor-. I nun 4 to 7 day-. Record- \\eie also made of o\ er I ,OOO 

 Kir\.e. The average larval life i- :M> da\'s; but, a- in tin- case 

 of the hat chini; time, tin- period may be shortened to 17 days or 

 extended o\ er 24 da> - b> ditfeiences in external conditions. 

 The ,i\ pupal period i-, u days, though adults frequently 



emerge in a -horter time, and a few do not escape until 13 or 14 

 day- have elapsed. These variations in the duration of the dif- 

 ferent stages may occur in eggs, larvae or pupae from different 

 batches of eggs or from the same batch. 



