126 The Ohio Naturalist. [Vol. IV, No. 6, 



The mouthparts of a number of larvae were examined (Figs. 

 loi, 102), and all were practically the same; salivary or other 

 gland structures could not be demonstrated. 



I am inclined to believe that the Cecidomjnd galls are due to 

 purely mechanical stimuli and that the great variations are due 

 to the different tissues upon which the larvae feed. 



Mr. W. A. Cannon,-'^ in discussing a Cecidomyid gall on the 

 Monterey pine, says that the "larvae take their food only by 

 absorption through the surface of the body," also that " there is 

 no indication that the hypertrophy is either caused or affected by 

 any substance deposited with the eggs." 



3. HYMENOPTERA. 



We now come to the galls of greatest complexity and also to 

 those with which we have the greatest difficulty. These galls are 

 so very generally infested with parasites and inquilines that it is 

 difficult to decide which larva is the true gall producer. 



A careful study of these shows that the insects have a very 

 strong pair of mandibles (Figs. 103 to 108), each working upon 

 two pivotal points. Some of these mandibles appear to have an 

 opening at the tip (Figs. 104, 105), and some showed what 

 appeared to be sacs or glands at the base (Figs. 104, io6b). In 

 one case at least (Fig. 104) these glandular sacs appeared to be 

 connected with the opening. The question that naturally pre- 

 sents itself is, are these openings for the purpose of pouring out 

 a fluid or are they suctorial as in the case of Chr3'Sopa and other 

 families ? In only two species was it possible to demonstrate 

 these structures. Some light is thrown upon this b^- Part VIII, 

 in which it was shown that the cell walls of the inner or nutritive 

 zones were not destroyed, but that the contents of the cells were 

 removed, causing them to shrivel. 



The teeth of the mandibles are never on the same plane and 

 the mandibles become more and more chitinous as the larvae 

 approach maturity. The strength of the mandibles appears to 

 depend upon the density of the tissue through which the insect 

 works its way to the outside In A. inanis (104) and A. con- 

 fluentus (Fig. 105) the strength of the mandibles is practically 

 the same and the character of the galls very similar. In D. sim- 

 inis (Figs. io6a, b) the mandibles are stronger and the tissues of 

 the gall correspondingly denser. C. petiolicola (Fig. 103) is by 

 far the strongest of thOvSe studied, and the tissues through which 

 the insect must work its way the densest of the leaf galls (Fig. 

 124). 



A sttidy was made of the larvae from galls of C. papillatus. 

 This is a small, rather dense leaf gall. Larvae of two species 



'"Cannon, W. A. "The Gall of the Monterey Pine." The American Naturalist, Vol. 

 XXXIV, No. 406 (Oct., 1900), p. Soi. 



