82 The Ohio Naturalist. [Vol. XIII, No. 5, 



respiratory appendage (Figs. 84, 85) is a fourth longer than broad, 

 testaceous brown, ringed about mid-length, thence slightly 

 constricted. The spiracles {a) moderately long, somewhat ele- 

 vated above the surface; the inter-spiracular spines {b) short, 

 blunt, spur-like, rather prominent. Dorsal spiracular spine [c] 

 short, compressed; its breadth about equal to diameter of the 

 approximate circular plate {d). 



These larvae were found, full-grown, at Cedar Point, July 7, 

 1911. The larval stage continued indoors to July 11 and 12. 



They were collected on the Poplar or American Aspen 

 (Populus treniuloides Mx.) in the well-known, characteristic galls 

 on the ends of the twigs, made by the aphid, Pemphagus vagabundus 

 Walsh. 



These galls are large, commonly two inches in diameter, very 

 irregular in shape, the outer surface thrown into numerous deep 

 convolutions. Their structure is such that they enclose a number 

 of small, partially separated chambers, the thick walls of which are 

 lined by the aphids. 



There are usually several openings to the many-chambered 

 gall, but it is pretty certain that the larvae do not ordinarily 

 migrate from gall to gall; although there is a bare possibility that 

 they might do so if the food supply in any one ran out. They 

 are negatively heliotropic, seeking out protected dark comers 

 when kept in confinement. They feed on the body contents of 

 the aphids; hence there is commonly an abundance of food at 

 hand and, as the volume of the chambers in the gall is small, there 

 is no occasion, and little opportunity, for active movements. In 

 correlation with this we find the larvae very sluggish, lying quietly 

 for hours or even days, even though unfed. Since migration 

 from one of these galls to another would commonly involve trav- 

 eling for several feet, it seems to me very likely that the larva or 

 larvae are dependent on the aphids within the single gall in which 

 they begin their larvab existence. They are very well protected 

 within the poplar galls and I found no parasites affecting them. 

 It would seem that they are paying for their well-fed, well-pro- 

 tected, sedentary life in sluggishness, and are possibly on the road 

 to degeneration. 



Pupa. 



Dimensions, average of 5: Length 7.2 mm., height 3.5 mm., 

 width 3.8 mm. These puparia (Figs. 86, 87) are exceptionally 

 inflated dorsally, the ratio of height to length being greater than 

 in any of the other species I have examined. It is characteristic of 

 them also that the posterior inflation is equal to, or greater than, 

 that anteriorly; in outline, as seen from the side, the dorsal half 

 of the ])uparium makes an almost perfect semi-circle. The ven- 

 tral line is sinuate. The respiratory appendage (a) projects from 



