8 CLASSIFICATION OF THE ALEYRODIDiE. 



It would appear from this that Peal considered the. vasiform 

 orifice as a special secreting structure and honeydcw to be connected 

 in some way with the circulation. Miss Bemis seems to have a some- 

 what similar idea about the lingula, for she says,* " In some species 

 there are seen minute, blunt tubes on the apex of the lingula through 

 which the fluid may be secreted." 



In the introduction to a paper on Aleyrodidas ^" Tullgren dis- 

 cusses the vasiform orifice. His idea of its nature seems to be the 

 correct one, but he does not go into detail, and we believe him wrong 

 in calling the vasiform orifice the anal opening, for the anus proper 

 seems to open within it. 



In the forms examined by us the anus appears to open below the 

 lingula (PI. II, fig. 5) which functions as the supraanal plate. AVe 

 are unable to find a definite opening at the tip of the lingula. In 

 any case, whether the anus is always at the base or sometimes at the 

 apex, as in the Psyllidse, this in no way alters the standing of the 

 lingula, which would in either case be the supraanal plate. The 

 operculum is a little more difficult to place. It would not appear 

 strange if it were believed to correspond to the rudimentary last 

 abdominal segment in the Aphididse, as suggested by Tullgren, for 

 its position in regard to the anal plate is very similar. It does not, 

 however, often appear as a distinct segment, but looks like the 

 rolled-back edge of the lingula. 



The substance known as honeydew is, as implied above, merely the 

 excrement of the insects. It is deposited in large quantities by the 

 larva^^j pupse, and adults and forms a medium for the growth of 

 several fungi. The early pupa? excrete much more than the late 

 pupae, while the larv?e, in the earlier instars, excrete the most of all, 

 the substance being ejected once or twice for every minute, although 

 not always at regular intervals. The salivary glands are tAvo rounded 

 bodies situated one on either side of the head and united by small 

 ducts. 



The exact nature of the wound of the puncturing setae of Aley- 

 rodidse we have not ascertained, but in all probability it is similar to 

 that made by the Aphididac and the Coccidae, where the setae pass 

 around the outer cells and finally puncture the soft bast cells from 

 which the proteid content is taken. These proteid substances form 

 the bulk of the insects' food, while much of the sugars taken in at the 

 same time are passed out as honeydew. 



THE WINGS. 



The wings are first noticed in the late embryo as imaginal disks 

 produced as ingrowths of the hypodermis. These, losing their con- 

 nection with the outer layer, soon take on the appearance of closed 



