ARTHUR DEWITT WHEDON 413 



The Muscular Diaphram (plate XXIV, figure 14) is like that 

 of the Aeshnids in form ])ut it is attached in the extreme anterior 

 end of segment four. This places two whole segments instead 

 of one between it and the Subintestinal Muscle. As it bows 

 backward most of this distance, its contraction and flattening 

 may be one of the causes of the gizzard being so often in the 

 thorax. 



Morphology of Odonate Imagoes 



A great deal of attention has been paid to the thorax of the 

 adult dragonfly, but very few references to abdominal structure 

 can be found. Its general structure is of course included in such 

 treatises as those of Calvert (1893) and Tillyard (1917); work 

 upon the abdomen is otherwise scattered through special papers. 

 Cuvier ("Le Regne Animal") as far back as 1834 figures the 

 simpler internal structure of Aeshna forcipata Fab. Plateau 

 (1884) has described briefly and figured the muscles of a few 

 segments of Agrion mnguineimrm his study of respiratory move- 

 ments. Fenard in 1896 gave an account of the repioductive 

 organs of Lihellula depressa and reviewed the work of others on 

 Libellula and Aeshna, and Marshall (1914) reworked the anatomy 

 and histology of the digestive tract and reproductive organs of 

 Libelhda quadrimaculata. 



The following work upon representatives of the subfamilies 

 Agrioninae, Pseudostigmatinae, Aeshninae, and Libellulinae con- 

 tains very little that is new beyond the study of many more types 

 than have heretofore been used and the resulting material for 

 comparison of variations. A dissection of the female of so elong- 

 ated a form as Megaloprepus coerulatus should be of value in a 

 discussion of the functions of the abdomen. 



The dissection of the material was carried out about as with 

 the larvae. Freshly killed specimens were used whenever the 

 seasons permitted. At other times material in 70 per cent or 

 83 per cent alcohol was used. This greatly increased the diflft- 

 culties which at best accompany the dissection of such slender 

 forms as the Zygoptera: many specimens are required in such 

 cases to assure the working out of the systems. 



I. Zygoptera. Agrioninae, Pseudostigmatinae and Lestinac 

 Calopteryx maculata was here used (plate XXV) as the type 

 and the other species dissected for comparison. 



TRANS. AM. ENT. SOC, XLIV. 



