stough: the hackberry psylla. 139 



Pachypsylla, and a careful comparison of the two forms would 

 throw much light on the question. 



The metathorax is not so heavily braced as in Pachypsylla, 

 but the coxal region is still well developed. A study of the 

 psyllid pupa would probably show much of interest in this con- 

 nection, as these parts above mentioned are all represented 

 there but somewhat simplified. The folding and fusion of parts 

 in the adult, and the presence of a heavy, braced endoskeleton 

 and the complex articulation of the trochanter of the meta- 

 thoracic leg, are all specializations to render possible and in- 

 crease its jumping power. 



My studies on the thorax of the Psyllidse agree with the 

 recent articles by Snodgrass (1909) , in which the old theory of 

 Audouin making each tergal segment to be composed of four 

 primitive sclerites is discredited; I have been able to find no 

 more than three sclerites composing the mesoterga and hieta- 

 terga. 



WINGS. 

 I. VENATION. 



The wing venation of the Psyllidse seems never to have been 

 reduced to any uniform system such as that of Comstock and 

 Needham (1898-'99). I find the venation figured by Mally, 

 Edwards, Slingerland (1896) and others, but the nomencla^ 

 ture is not uniform and is of a special nature. I have at- 

 tempted to reduce the venation as seen in the insect under dis- 

 cussion to the system of Comstock and Needham, above 

 mentioned. In this study my first conclusions as to the homolo- 

 gies of the veins were arrived at through the study of adult 

 wings alone, but later I have made use of nymphal wings and 

 wings of newly emerged adults. 



On March 6 a large number of pupae of Pachypsylla celtidis- 

 gemma were procured from their galls on the stems (lateral 

 buds) of the hackberry, some seven or eight being found in 

 each large-sized gall. Their wing pads, after soaking for about 

 a day in dilute formalin, were removed, mounted in dilute 

 glycerine, and studied with special reference to their tracheae. 

 As soon as I had begun this study I found that my conclusions 

 arrived at earlier were borne out in almost every detail by the 

 number, position, character, etc., of the tracheae of the 

 nymphal wings, these tracheae corresponding to the veins of 

 the adult wing. 



