Oct., 1920 Bulletin of the Brooklyn Entomological Society 95 



Chironomidse, the pigment is hemoglobin, Hke that of vertebrates, 

 except that it is found in the plasma, and not within the cor- 

 puscles. The morphology of the blood gills is extremely simple. 

 The gills consist of sacs everted from the body. They have a 

 very thin cuticle, and a hypodermis, and their lumen is continu- 

 ous with the h^mocoel, so that blood can freely flow into the 

 sacs and out again. The oxygen diffuses through the epidermis 

 just as in the case of vertebrates and is fixed by the hemoglobin 

 or other carrier (perhaps hemocyanin?) in the blood. Just what 

 this other carrier may be is not definitely ascertained. But by 

 far the larger number of aquatic insects have no visible colored 

 carrier or respiratory pigment. Thus, for example, Trichoptera 

 larvce, the larvae of Simulium, of Culicidse, and of most Chi- 

 ronomid^, have gill pouches, usually placed at the caudal end, 

 but all without any visible indication of a respiratory pigment. 

 There is need of more work on this phase of the subject. 



4. Transportation of Air to the Tissues. 



The question of how air is taken up by the cells is still in doubt. 

 Portier claims that the tracheoles end blindly in the individual 

 cells, according to observations made with polarized light. Then 

 there is the older claim that they end blindly at the cell walls, and 

 there is the newer supposition that the tracheoles form capillary 

 loops similar to those at which oxygen enters in the gill lamellae 

 and also similar to the capillaries of the vertebrates, and that the 

 oxygen passes very readily out through the capillary wall and 

 cell membrane wherever needed. All three theories remain to 

 be proven. But the general cycle of air absorption and transpor- 

 tation can be outlined readily. There are several types of cycles. 



a. Atmospheric air — enters tracheae and tracheoles — passes 

 into solution in cell cytoplasm (all terrestrial insects, all surface- 

 breathers) . 



b. Atmospheric air — passes into solution in water — passes 

 through membrane and tracheal wall — goes out of solution in 

 lumina of tracheae — passes into solution in cell cytoplasm. Hence 

 twice in gaseous form and twice in solution till used. (All 

 water-breathing hemimetabola, all Trichoptera larvae and pupae, 



