1918.] NATURAL SCIENCES OF PHILADELPHIA. Ill 



fairly closely to that of the other species studied in the papers by 

 CuUen, Jamieson, Carroll and Calvert. 



Whether the air which enters the rectum is carried from it by 

 the tracheae or whether it diffuses through into the spongy tissue 

 in contact with the basement membrane of the rectum and is then 

 carried by the blood to the different parts of the body, is at present, 

 rather difficult to say on purely physiological grounds and will 

 require more intensive study. 



From a morphological study of the species of larvae used in my 

 experiments, carried out in a way similar to those of Calvert, 

 Jamieson, Cullen and Carroll, I find that the number of tracheae 

 and of tracheoles, distributed to the rectum is very small — much 

 too small to supply or take up sufficient oxj'gen for the respiratory 

 needs of the larvae. Doubtless the greater part of the oxygen 

 diffuses through the spongy bands as suggested by Carroll. 



If oxygen from air in the water diffuses through the walls of the 

 rectum and is taken up by the blood and is thus distributed to the 

 various parts of the body, the tracheae and tracheal trunks must 

 be accessory structures, since otherwise the oxygen would have to 

 be taken up by them from the blood and be distril:)uted by them 

 to the various parts of the body. This is hardly conceivable, since 

 the blood is found to circulate freely to all parts of the body. One 

 fact which would point to such a function of the blood is, that the 

 heart's action when subjected to different gases, is not interfered 

 with until after violent contractions of the rectal wall have taken 

 place, showing that possibly the gas is carried cUrectly to the heart 

 by means of the blood and not by means of the tracheae. On the 

 other hand, from morphological studies already cited (Calvert, 

 Cullen, Jamieson and Carroll) we see that the tracheal supply to 

 the rectum and especially the manner of ending of the tracheoles, 

 would seem to indicate the possible diffusion of the oxygen through 

 other places than those where these tracheoles end (Carroll). If 

 such a condition is found, the problem becomes one quite different 

 than heretofore supposed — the tracheoles and tracheae then must 

 play only a secondary ro'e in the distribution of oxygen to the body 

 if at all; the blood must be the important means of transportation 

 of oxygen either to the tracheae, or directly to the various parts 

 of the body. 



. Tilly ard (1916) says regarding the mode of diffusion of air in 

 Zygopterous larvae: "The diffusion of CO- outwards into the rectal 

 water supply, and the diffusion of air inwards, is undoubtedl}' effected 



