MORPHOLOGY OF THE ALEYRODIDJC. 7 



sclerltes are present, arranged similarly, though somewhat differently shaped. 

 The labrum is much shorter and smaller proportionately than in this family, 

 and the setae seem to be relatively shorter. The end of the labium has the 

 same lateral processes, but these are relatively smaller. The Aleurodid labium 

 has a bend similar to that of Pachypsylla. 



THE DIGESTIVE SYSTEM. 

 (PI. II. fig. 2.) 



Our observations on the digestive system of the adult are as fol- 

 lows: Leaving the mouthparts the pharynx is met with as a narrow 

 tube which j)asses gradually into the oesophagus. In the metathorax 

 there is a distinct enlargement, the midintestine, and from this are 

 given off two large saclike structures. From Gary's Avork ^ we con- 

 sider these gastric csecse, for he says, "After the dorsal wall of the 

 enteron has closed a pair of diverticula are given off from near its 

 anterior end." The midintestine is looped, as shown in the illustra- 

 tion, and joins the hind intestine in the anterior part of the body. 

 This latter is narrow but is more dilated caudad of the vasiform 

 orifice, Avhere the anal opening occurs. 



The nature of this orifice in the immature stages and the function 

 of the lingula seem to have been imperfectl}^ understood by some 

 recent writers. The older writers, however, apparently had, in gen- 

 eral, the correct idea of it. Westwood, for example, in his descrip- 

 tion of Aleyrodes vapor ariorum^^'^ speaking of this structure, says, 

 " With the anal apparatus placed at some distance from the hinder 

 end of the body." 



Peal, in 1903, discussed this structure at some length, "We quote the 

 following from his paper r^^ 



Some time back, while I was examining an aleurodid which in its earlier 

 stages is remarkably flat and transparent, I was fortunate enough to observe 

 the lingula in motion. This organ was shot out beyond the vasiform orifice 

 with extreme rapidity, it being protruded some four or five times a second. 



When the lingula was shot out, the vasiform orifice moved in unison, the 

 upper edge being bent inwards while the whole organ moved caudad. The 

 internal opening of the lingula lies directly in the path of the mdiniontary cir- 

 culatory system, and when the organ is in motion it throws the circulatorj' 

 fluid into a pulsating motion for some distance within the body cavity. I have 

 been unable, so far, to detect the actual formation of the globules of honeydew, 

 but as soon as the lingula comes to rest after a series of protusions a small 

 globule may be seen just within the lower end of the lingula. This globule 

 advances slowly, being apparently forced forward by the movement of the 

 lingula. and after awhile reaches the tip of that organ I have never observed 

 these globules within the lingula of an adult insect, but once on examining an 

 adult male of Aleurodes Simula, I perceived a globule of honeydew emerging 

 from the lingula. 



There is no doubt that the function of the organ is the secretion of honeydew 

 and the oijerculum may be regarded as a protective covering to this organ. 



