1912] Morphology and Biology of Insect Galls 311 



Galls produced by the Stagmatophora moth were examined a few- 

 days later and the larvse were found to be passing the winter under 

 very similar conditions to those described in the case of the Eucosma 

 species. The Stagmatophora larvae were not perfectly dormant, how- 

 ever, and soon became quite lively in a warm room. They were found 

 invariably in the gall cavity with their heads a short distance below the 

 prepared exit. This had been constructed as in the preceding case and 

 was situated at the same place. The silk lining covered the interior of 

 the gall but in this case was gradually narrowed to the size of the hole 

 around the edges of which it was attached. As the plant stem was not 

 hollow above the gall, the roof of the gall cavity occupied much the same 

 position as the slanting silk partition in the Eucosma gall. 



The silk lining common to both of these galls helps to prevent the 

 loss of moisture and the consequent desiccation of the larva. 



The cross partition of the Eucosma gall and the tapering neck found 

 in the lining of the Stagmatophora species seem to have the function in 

 common of guiding the occupant of the gall to the prepared exit. 



Memythrus tricinctus Harris. 



This form has hitherto never been considered a true gall maker — 

 just why it is difficult to understand. Beutenmiiller^ reports it as 

 a borer in stems of poplar and willow and in galls of Saperda concolor. 

 I have repeatedly, however, bred this species from swellings on the 

 smaller branches of young trees of Populus tremuloides Michx. These 

 swellings were spindle-shaped, gradually tapering at each end to the 

 size of the normal stem. In external form they were quite typical galls 

 of the Lepidopterous class. 



A comparison of the larval chamber of this gall with that of the 

 Eucosma species shows that the two have certain features in common. 

 Thus, although the opening in the stem made by the young larva in 

 entering closes in the Eucosma gall, but not in this one, it can be found 

 in the earlier stages of both. The silk lining in the larval chamber is not 

 present, but the slanting silk partition has a similar structure and position 

 to that found in the Eucosma species. This partition shuts off the per- 

 manent larval entrance from the part of the chamber in which pupation 

 takes place. The place of exit has the same relation to this partition as 

 that described in the Eucosma gall. The opening is prepared in the same 

 manner. The larva eats through the wall of the gall until the part re- 

 maining is translucent just as in the case of the Eucosma or Stagmato- 

 phora forms. The larvse in the two latter species prepare this opening 

 in the fall, but the Memythrus larva does not complete it until shortly 

 before pupation in the spring. 



