SOME PARASITES OF SIMULIUM LARV.E. 



It will be seen from these cases that in every instance they 

 occurred in artificially reared larvae, and it is probable that the 

 prothetely was due to an increased temperature, perhaps with 

 the aid of abundant food, in some way hurrying on the develop- 

 ment of the histoblasts. 



This fact suggests that the histoblast- may be cau-ed to 

 develop, though at a much slower rate than the larval organs until 

 pupation, by some enzyme secreted by the in-ect and that they 

 can develop only as t'a-t a- thi- -timulant is formed. Ii- -upply 

 tlm- acts .1- a regulator. An increa-ed temperature i- in nio-t 

 d\ antag< u^ to en/yme action and in thi- case it i- prob- 

 able tli.it it either causes more of the en/yme to be -ecreied or 

 -tiinnlate- the action of the amount already available. 



I ). v 5 , after numerous experiment- <m retardation and 

 a i eleration of development and pupation arrived at the tol- 

 li. \\iiu i "in lii-ion-: Development and pupation are caii-ed by 

 enzymes \\hich are not very evident in the early lar\.il 



The\ , lio\\e\ei. increase \\ith the growth ot tin- larva until ii- 

 |)upation. ,n \\hich period they are at their maximum -tivnvjh; 

 tin \ then begin to dimini-h. till at the end of the pupal period 

 their action entirely ceases. He also state- that the en/vine 

 action can be hindered by the presence of another bl\ . and that 

 by obtain! IK' an en/yme of an increased strength before pupation 

 de\ el"pnii-ii! can be abnormally accelerated. 



I 1 i- exident that the cells of the hiMobla-t- .in- can- d to 

 dexelop b\ a different stimulus from that \\hich causes the de- 

 \ elopineiii of the larval organs, for in the former case d-\ elopmeiit 

 i- \ei\ -lo\\ during the larval stage, \\lu-n the latter organs are 

 de\elopin. rapidly, and it is only when the-e ha\ ir.irhed 

 their limit of de\elopment at pupation, that the adult organs 



n in de\ (lop \\ ith an\ rapidity. 



Thi> suj - that there may be in the insecl body t u o sets 



of eii/> me- \\hich one may term "larval" cn/yme- and "ima:;- 

 inal " enzymes. The-i- are -ulficiently different so that condition-, 

 which cause ;he ac. -el. -ration or retardation of one of them n< ed 

 not ne(e--aril\ h.i\e an\ effect on tin- oilier. It thi- be SO, one 

 ha- a probable explanation of prolhetely and al-o. a- I -hall 

 attempt to -how in the l'ollo\\in;c paragraph-, ol metal heteU. 



