l895-] ENTOMOLOGICAL NEWS. l8l 



Preliminary Notes on the Youngest Larval Stage 

 of some Odonata. 



By Philip P. Calvert. 



Availing myself of the facilities afforded by the Biological 

 School of the University of Pennsylvania, I have recently studied, 

 by means of sections and otherwise, the external and internal 

 structure of the larvae of Gomphus exilis Selys and of Libellula 

 pulchella Drury as it is immediately after hatching from the ^^g. 

 The larvae were obtained by capturing the females while oviposit- 

 ing, collecting the eggs in a tumbler of water and allowing them 

 to remain undisturbed until hatched. The detailed results of 

 these studies, it is hoped to publish later; a very brief summary 

 of some of them follows, and only such facts as are believed to 

 be new are mentioned,* It is my intention to eventually study 

 the entire embryonic development of these insects. 



In both species studied, the divisions of the alimentary canal, 

 fore-, mid- and hind-gut, occupy relatively different positions 

 from those of the old nymph and imago, in that the fore-gut ex- 

 tends only as far as the second thoracic segment, the mid-gut from 

 the third thoracic to the third or fourth abdominal, the hind-gut 

 from the latter point to the apex of the abdomen. It follows, 

 therefore, that during larval development the three parts of the 

 alimentary canal undergo a shifting backwards, accompanied by 

 a relatively great decrease in the length of the hind-gut and, cor- 

 respondingly, a relatively great increase in that of the mid-gut. 

 This is correlated with the great increase in the length of the 

 middle abdominal segments at transformation, due to the neces- 

 sity for a long rudder or steering-apparatus behind the wings for 

 the preservation of equilibrium in flight. No similar shifting of 

 the abdominal ganglia occurs. 



In both species there are three, and only three,! Malpighian 

 tubules present, ofapproximately equal length (.3 — .35 mm.), and 

 three rectal glands. In L. pulchella , in front of the latter, are 

 the beginnings of six rectal gills, but in G. exilis, with a longer 

 embryonic period (216 to 240 hours, as compared with 144 to 



* A summary of the information then existing in regard to the structure of the youngest 

 larvae of the Odonata is given by the present writer in Trans. Am. Ent. Soc. xx, pp. 195-6, 

 October, 1893. 



t For a recent discussion of the Malpighian vessels of insects, see W. M. Wheeler, 

 " Psyche," May to December. 1893. 



