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remarkable also in this connection, that the whole development from egg to imago 

 can be completed in the course of only four days. From a biological point of view 

 it is highly interesting that the development of the very same species dependent on 

 outer conditions, in the one case can be completed in the course of four days, in 

 the other in the course of many weeks; further that among the mosquitoes there 

 are species which finish their whole development in four days, others which nor- 

 mally spend about eight months either in the egg-stage or in the larva-stage. 



HEIMANN (1913 p. 31) has shown that the sex differentiation with regard to 

 C. pipiens takes place already at a very early stage of the development; cut series 

 show that already in larvse of 2 mm differentiations between ovaria and testes may 

 be shown; it may be pointed out that the observations were made upon a species 

 the larva of which only lives a few weeks and perhaps only a single w r eek. It 

 ought to be investigated whether the rule also holds good for larvae which live for 



