THE JUMPING PLANT-LICE OR PSYLLID^ OF THE NEW WORLD. 3 



these external parts. In the following pages a brief discussion of 

 the homologies of the sclerites is given, with an explanation of the 

 terms used in the systematic portion of this work. 



MOEPHOLOGY. 



Anatomical studies on the family Psyllidae are not numerous, but 

 in proportion to the systematic work on the group they are quite 

 extensive. All of this work has, however, been based on a relatively 

 small number of species and therefore the results are not entirely 

 accurate. 



The most extensive of these works was by Emmanuel Witlaczil 

 in 1885, Die Anatomic der Psylliden. The largest and most impor- 

 tant part of this paper is on the internal anatomy, with a relatively 

 small part on the external morphology. He discusses in more or 

 less detail the following subjects: Segmentation of the body wall, 

 musculature, wax glands, tracheal system, nervous system, digestive 

 canal, circulatoiy system, reproductive organs, and finally the 

 relationships of the family to the other groups of Ilomoptera, both 

 the Phytophthires and the higher groups. 



Loew ('76:187-194) discusses very briefly the external anatomy, 

 but in a very general way. H, B. Stough ('10:121-165) has more 

 recently studied the morphology of the hackberry psyllid, Pachypsylla 

 c.-mamma Riley. This latter work is not altogether satisfactory 

 from the point of view of clarity and definiteness, and also shows 

 several errors in the intei-pretation of sclerites. It may be stated, 

 however, that the species of Pachypsylla are among the most difficult 

 for the purpose in view — of homologizing sclerites of Psyllidae with 

 those of other Homoptera — and this may account for the errors. 



Some very good work has been done by Miss Patch ('09:117-121) 

 on the wing veins of Psyllidae, homologizing them with the veins 

 of Aphididse, Coccidse, and Aleyrodidse. The Comstock-Needham 

 system of nomenclature of veins as applied to many other groups of 

 insects has been applied here by Miss Patch. Because of its sim- 

 plicity and superiority in all ways the same nomenclature is followed 

 in the taxonomic work of the present paper. 



No attempt has been made by the writer to go into the internal 

 a,natomy of the Psyllidse; nor is the external morphology presented 

 in as much detail and completeness as would be desirable if the 

 scope of the present work were not so limited. There are many very 

 curious and remarkable developments in the members of this family, 

 and several sclerites which are difficult to homologize satisfactorily 

 with other Homoptera. These must be studied more carefully 

 before the conclusions can be relied upon with absolute certainty. 

 Certain phases, therefore, of the external morphology are presented 

 in somewhat of a tentative manner. 



