THE PUPAL STAGE OF CULEX. 19 



taken in at different apertures in the three states. The larva, accord- 

 ing to Raschke {op. cit.), breathes also by gills and by the rectum. 



I have already described the respiratory siphons of the pupa, and 

 given evidence to show that they really do lead directly into the 

 tracheae, in spite of Palm6n's contention to the contrary. 



From the base of each siphon, tracheae run to various parts of the 

 body and head. Amongst these may be mentioned specially one 

 transverse trunk running across the thorax between the alimentary 

 canal and the nerve-chain, and putting the two siphons in direct 

 communication with each other ; and a pair of longitudinal trunks 

 running backwards to the hinder end of the body, and giving off 

 branches to the various organs, and also a trunk to each of the 

 stigmata. As already mentioned, these stigmata are present in the 

 hinder region of the thorax, and in each of the first seven segments 

 of the abdomen ; but the stigmata, except the first abdominal pair, 

 are closed, and the pupal intima of the tracheie connecting them with 

 the main trunks is thin and collapsed. The widely open stigmata of 

 the first segment, with their spines and their probable function, 1 

 have already commented upon ; but while insisting on the importance 

 of the hydrostatic function of the tracheal system in both larva and 

 pupa, I would again say that I do not consider this a sufficient 

 ground for the view that the hydrostatic function is the primitive 

 one. In Culex larva and pupa, it is important only inasmuch as it 

 subserves respiration by bringing the animal to the surface and 

 maintaining it there in the only position in which air can be breathed 

 directly. 



The cuticular lining ("intima") of the chief trunks and their 

 branches is well developed even at the commencement of pupal life, 

 and has the usual spiral thickening. The trunks connecting the 

 stigmata with the main trunks are the only ones that undergo any 

 marked change during the pupal condition. These widen around 

 their separated and collapsed intima, and a new and strongly 

 thickened intima is formed. In the main trunks no new intima is 

 formed, and when the imago escapes from the pupal cuticle no 

 portion of the intima is shed from any part of the system which has 

 been functional during pupal life, excepting the portions connecting 

 the siphons and the first abdominal stigmata with the main trunks. 

 These fragments are, in the case of the siphons, well developed, and 



