p. K. AwATi 261 



(ii) Tracheal system in the larvae (Fig. 15). This system is extremely 

 complex. There are various devices between the external opening and 

 the tracheal trunk, which are: 



(a) The spiracles (three on the abdomen and two on the thorax) 

 are situated in a pit which is covered over with long hairs. 



(6) The external lid of the spiracle. This is formed by a thick 

 process which lies across the spiracle. 



(c) The closing apparatus. It consists of thickened chitin stretching 

 from the one side of the tube to the other. It is acted upon by the 

 spiracular muscles which are attached to this apparatus. When these 

 muscles contract, this transverse bar of chitin is pulled apart and the 

 spiracle is opened. 



{d) Atrium. Below the closing apparatus is a cavity which com- 

 municates with the main tracheal trunk. 



The simple structure of the spiracle of the adult and the more 

 complex structure of that of the young lead one to infer the adult 

 will react more readily to an insecticide and this is actually the 

 case. In experiments with insecticides, I found that the adults 

 died as soon as the emulsion reached them, whereas the young 

 struggled for some hours before succumbing. The progress of the 

 insecticide into the adult is unchecked, whereas it is obstructed in the 

 larva; it has, in the latter case, to pass the hairs before it reaches 

 the spiracle, and it cannot then pass the closing apparatus till paralysis 

 is set up, opening the valve and giving it unrestricted entrance to the 

 tracheae. 



VIII. Reproductive System (Figs. 17, 18, 19, 20). 



(i) The reproductive system does not begin to develop until the 

 adult stage is reached, though the indication of this system is early seen 

 in the fourth and fifth instar, in which the external sexual differences 

 begin to be visible; the males (the larvae which are going to become 

 males) being short and the females longer. 



(ii) Couplitig. Coupling begins in the first week in June, but the 

 eggs are not laid until September. The coupling members lie side by 

 side dorso-ventrally, their heads being turned in the same direction. 

 This is a very characteristic position of these insects. 



(iii) The re])roductive organs of the female. Primary. These con- 

 sist of the following parts (Figs. 18, 19, 20) : 



(1) Ovaries (Fig. 19). They consist of small egg-tubules, from 



18—2 



