1 91 2] Morphology and Biology of Insect Galls 361 



traced until it passes over into the inside layer of the nutridve zone 

 (Fig. 49). This canal can scill be detected in well-grown specimens. 



Only mature material of Andricus piger Bassett and Andricus 

 petiolicola Bassett was obtained, and while the canals with the epidermal 

 lining are well marked, they are shut off from the larval cavity by out- 

 growths of sclerenchyma from the protective sheath (Figs. 43, 44). 

 There is little doubt, however, but that in early developmental stages 

 they open into the gall cavity as in the genus Dryophanta. This view, 

 indeed, I have practically confirmed in the examination of an undescribed 

 species of Andricus on Quercus macrocarpa Michx. In this form the canal 

 is blocked at maturity by sclerenchyma (Fig. 47) as in the former species, 

 but at an early stage I have found it extending into the larval chamber. 



Summary. 



The evidence seems conclusive that there are two types of early 

 developmental stages of galls when the egg is deposited on the epidermis 

 of the host. The method of formation of the larval chamber as described 

 by Beyerinck is found in certain genera, as Dryophanta and Andricus, 

 while the method worked out by Weidel occurs in Neuroterus and in all 

 probability other forms. 



Feeding Habits of the Larv.<e of Gall Producers. 



With the exception of the family Tenthredinidae, all gall-producing 

 larvae have started to feed before the abnormal production of tissue 

 commences. The narrowing of the problem of gall production to the 

 influence of the larvae on the tissues of the host has given additional 

 importance to the problems dealing with the feeding habits of these 

 larval producers. 



Order Arachnida. 

 Fam. Eriophyidae. 



The members of this family have mouth parts of the sucking type. 

 With their cone-shaped beaks they pierce the cell walls and withdraw 

 the liquid contents. The cell walls are not used as food. 



Order Hemiptera. 

 Fam. Aphididae. 

 Fam. Psyllidae. 



The feeding habits of these families are similar to the preceding. 

 The possession of a suctorial proboscis makes it possible for them to ob- 

 tain the liquid contents of the cells by merely puncturing the walls. 



Order Lepidoptera. 



The larvae in this case consume the entire cells that line the interior 

 of the galls. 



Order Coleoptera. 



