80 PROCEEDINGS OF THE ACADEMY OF [March, 



of longer duration than the other two; 32 such sets per minute were 

 noted. At other times sets of five contractions were noted. In 

 some larvae, but not in all, the beginning of a set of rectal contractions 

 was often synchronous with a slight shortening of the abdomen; 

 the lengthening of the abdomen began before the contractions had 

 ended. A rhythmic shortening and lengthening of the abdomen 

 may perhaps furnish an indication of the existence of rectal con- 

 tractions in an opaque larva. Successive removal of the three 

 caudal gills in one larva was not followed by any immediate beginning 

 of rectal contractions, although such were seen four hours later; 

 the larva was not under continuous observation during all of that 

 time, however." (Calvert, Ent. News, XXVI, pp. 441-2.) 



In the diagram of the rectal tracheation of Thaumatoneura larva 

 figured by Calvert, Plate XVI, Ent. News, Vol. XXVI, there is one 

 area of rectal respiration supplied by the right and left dorsal rectal 

 tracheae and the right and left lateral rectal tracheae. It seems 

 from the structure of Argia putrida larva that there may be two 

 areas of respiration in the alimentary canal walls, a small one in 

 segment seven and a larger respiration area in segments eight and 

 nine. The respiration of the seventh segment may be carried on 

 through the tracheae supplied by the branches of the right and left 

 visceral tracheae. The larger respiration area of segments eight 

 and nine is supplied with tracheae through the branches of the right 

 and left dorsal rectal tracheae and the right and left lateral rectal 

 tracheae. In each case the structure of- the epithelium of the ali- 

 mentary canal appears to be the same. In the seventh segment, 

 the three patches of thickened epithelium supply the surface through 

 which respiration may take place. In the eight and ninth segments, 

 the thickened epithelium of the longitudinal rectal folds supplies 

 the surface through which respiration may take place (Fig. 1). 



At the present time there is considerable doubt in the minds of 

 observers as to the importance of these areas of respiration. When 

 the caudal gills have been removed, the Argia putrida larva continues 

 to live. Respiration may take place all over the surface of the 

 body through the thin body wall. If this is the case, then we may 

 assume that respiration also takes place throughout the length of 

 the hind gut through its wall. The numerous tracheae found 

 penetrating the thickened epithelium can be explained as necessary 

 because respiration is more difficult in these regions owing to the 

 thickness of the walls, hence the many tracheoles penetrating the 

 thickened epithelium. A comparison with the rectal respiration 



