32 PROCEEDINGS ENTOMOLOGICAL SOCIETY 



ECDYSIS IN THE DIPTERA. 

 BY FREDERICK KNAB. 



In a previous paper 1 I discussed the application of pressure 

 by means of imprisoned air by insects to effect their escape 

 from the egg aud from their exuviae. I showed that the em- 

 ployment of air in these processes is very general among in- 

 sects aud perhaps common to the entire class. Since then 

 other observations bearing on this subject have come to my 

 notice and I have seen several publications which were not 

 available to me at that time. There are a number of careful 

 observations on the process of eclosion of the imago in differ- 

 ent Diptera. These are of especial interest, as they bring out 

 striking differences in the two great groups of Diptera. Be- 

 sides most interesting differences of detail appear in the lesser 

 groups and in individual genera, and as the process itself is 

 not generally understood, it seems worth while to bring the 

 data together. 



In the paper referred to I already touched upon the fact 

 that there are two different modes of eclosion in the two main 

 groups of Diptera, the Orthorrhapha and the Cyclorrhapha. 

 The presence in the higher flies of a protrusile bladder, the 

 ptilinum, on the front of the head, and its function in bursting 

 the puparium, have been known since the time of Reaumur. 

 No such special organ exists in the Orthorrhapha, and I have 

 already shown that in the case of the mosquito escape from the 

 pupal skin is effected by inflation of the imprisoned imago's 

 entire body. However, I had not made a detailed study of 

 the process, or the manner in which the air is taken in and 

 where it is stored. I have since found that the process has 

 been well understood and carefully described by Dr. Adolph 

 Eysell. 2 A translation of Dr. Eysell's description will be given 

 elsewhere, so here it will only be necessary to indicate the 

 essential features. 



Some time before emergence a layer of air is deposited be- 

 tween the pupal skin and the enclosed imago. This layer of 

 air gives the pupa the peculiar silvery appearance which is so 

 characteristic of the end of the pupal period. Eysell states 

 that the air forming this layer is pressed out through the 

 stigmata of the imago; this is most probably true, as at the 

 time of ecdysis the tracheae contain no air. As the result of 



1 The R61e of Air in the Ecdysis of Insects. Proc. Ent. Soc. Wash. , 

 XI, 1909, pp. 68-72. 



2 Mense, C. Handbuch der Tropenkrankheiten, vol. 2, pp. 58-59. 

 (1905). 



