14 CLASSIFICATION OF THE ALEYRODID^. 



Psylliclic have a prominent bilobed pulvillus, while the Aphididae 

 have practicall}^ none. In some forms in the Aleyrodina) the paro- 

 nychium is very prominent, and in all forms it is represented either 

 by a pad or a spinelike structure. The paronychium in the Aleyro- 

 dida?, however, is never bilobed as in the Psyllidse, though in some 

 species there is a slight indication of this. 



WAX PORES OF PUPA CASE. 



The secretion of wax is very common in many of the Homoptera 

 and is particularly noticeable in the families related to the Aleyro- 

 didse, namelj'^, Psyllidae, Aphidida?, and Coccida^. In the Psyllidae 

 besides the anal wax glands there are in the larvae of many species 

 abdominal and marginal wax glands, the marginal ones of which 

 secrete long, fine, hollow, brittle, waxen hairs, which form a fringe 

 about the insect. In the Aphidida^ the glands are usually grouped. 

 In Schizoneura and some species of Pemjyhigus the secreting cells are 

 arranged in rings, while in Chermes, Miiulai-ius, etc., they are agglom- 

 erate in nature, and in some forms these agglomerate pores are sur- 

 rounded by a chitinized ring. 



In the larvae of the Aleyrodidse we have three types of pores, 

 namely, simple, agglomerate, and compound. In the Aleyrodinaj 

 the dorsal pores present are all simple, though many of them may be 

 larger than others and arranged in definite rows, producing a fringe 

 comparable to that in the larvae of the Psyllidae. It is in the Alcurodi- 

 cinae that the development of special wax secreting structures is found 

 and this development seems to throw some light on the relation of 

 the forms. In Dialeurodicus the dorsal pores are simple and usually 

 scattered, though in silvestril the greater number of them are col- 

 lected into a subdorsal band. In the species lahUlei these simple 

 pores have taken on a definite and restricted arrangement, forming 

 agglom^'ate pores as in some x^phididae. In the center of some of 

 these, however, is found a large, chitinous process which points to 

 these as near the forerunners of the true compound pores in Alcnrodi- 

 ciis. This fact, together with the shape of the lingula, wing, etc., 

 seems to indicate that lahillel is the type of a new genus older than 

 Aleiirodicus, but not so old as Dialeurodicus. In Aleurodiciis the 

 compound pores have a constant structure in all the species, indicated 

 in Plate III, figure 2. The chitinous ring surrounding the agglom- 

 erate pores in some other foims is here a definite elevated cup-like 

 structure. Within this cup the spinnerets are arranged in a ring 

 similar to the ring in Schizoneura., but, unlike these cells, are pro- 

 duced into more or less elevated rods or tubes. Within this ring of 

 spinneret rods is a chitinous process, apparently hollow, which may 

 be very long, as in holmesii, or as short as the outer cup. In Paraley- 

 rodes, while the pore is of the same compound type, it is different in 



