No. 39] ODONATA OF CONNECTICUT 23 



very greatly modified, but here again the sclerites corresponding 

 to other insects may be traced by means of internal invaginations 

 of the skeleton. Close approximation of the legs and reduced 

 area of the sterna are also confusing, and since both sternum and 

 notum of meso- and metathorax are little used in classification, 

 they will not be considered here. Along the anterior margin of 

 the mesonotum on either side is a very large spiracle, a long, 

 narrow slit near the mid-dorsal line, under the caudal margin of 

 the pronotum. Just behind each spiracle in the Zygoptera there 

 is a small plate known as the mesostigmal plate or lamina, which 

 varies in some genera and afifords a valuable means of determin- 

 ing the females of these groups. The most conspicuous spiracle, 

 however, is located at a point near the dividing line between meso- 

 and metathorax, on the anepisternum of the metathorax. This 

 spiracle is smaller in size and elliptical or circular in outline. In 

 front of the anterior wing bases are two small plates, the paraptera. 



The wings and legs of Odonata are comparable to other insects, 

 and the nature of both appendages is of great importance to 

 systematists. The legs are composed of the following segments 

 beginning with the proximal: coxa, trochanters (two segments), 

 femur, tibia, tarsus (three segments). There are always two 

 claws attached to the tip of the tarsus. Various shapes and sizes 

 of setae are borne on femora, tibiae and tarsi. 



The wings are apparently complexly veined, but analysis of the 

 system of venation proves it to be homologous to that of other 

 insects. The great number of supernumerary cross-veins is indeed 

 confusing at first sight, but it is possible with a little study to 

 follow the course of the larger primary veins and, when once 

 acquainted with the general scheme, to find the characters for 

 identification. Needham and Comstock attempted to homologize 

 the veins with other insects, and their system for the Odonata has 

 been accepted until recently. Tillyard and Lameere,'' however, 

 believe that the original interpretation of Comstock and Needham 

 is in error because of the disappearance of certain veins in the 

 center of the wing, and they have modified the original interpreta- 

 tion to allow them to fit it more closely to the fossil record and 

 also to other orders related to the Odonata. 



Beginning with the fossil cockroaches of the Carboniferous 

 period — in all probability the progenitors of modern insects — the 

 wings contained a large number of veins. As conditions changed 

 at the close of this geological period, the wings of many species 

 became narrower, and there was an accompanying decrease in size, 

 probably due to changing climatic conditions. At this time the 



" Perhaps the best expression of Tillyard's recent ideas along this line is found in the 

 American Journal of Science, Vol. ix: 328-32: 1925, and Vol. x: 68-73: 1925. A 

 translation of Lameere's work is found in Psyche xxx: 123-32: 1923. See also Insects 

 of Australia and New Zealand, pp. 67-71 : 1926, by R. J. Tillyard. 



