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



O. S., Holcaspis centricola O. S., Dryophanta palustris O. S., 

 and Callirhj'tis papillatus O. S. In these cases it is evident that 

 the force necessary to penetrate the bud may be as great or even 

 greater than the force uecessar}' to penetrate a stem. Adler's 

 observations demonstrate that great force is used to penetrate the 

 buds and reach the desired point for depositing the eggs. 



Beyerinck has demonstrated that the fluid ejected by the ovi- 

 positor of the Cynipidae is very different from the fluid ejected 

 from other Hymenopterous insects ; that it is without taste or 

 smell and does not irritate when injected under the skin. Adler 

 has demonstrated that this fluid cannot be considered as the stim- 

 ulus to gall production. It is probable that it may serve to attach 

 the eggs, or as an antiseptic, or as a seal for the wound. 



Since the gall does not form until after the hatching of the 

 larva it is evident that oviposition does not furnish the stimulus 

 unless it maj^ be that there is cell division but no swelling of the 

 plant tissues previous to the hatching of the larva. The author 

 has made no observations upon this point. Adler, in discussing 

 this question, says, in regard to Trigonaspis : " This fly pricks 

 the leaf in May, but months pass before au}^ trace of gall forma- 

 tion can be seen. It has tolerably strong ovipositor with which 

 it cuts into the veins of the leaf, and in this way a distinct mark 

 is left wherever an egg has been inserted. Guided by these 

 marks it is easy to find the egg, but it is not until September that 

 the larva leaves the egg, and then gall formation begins." 



MOUTHPARTS. 



Since oviposition does not give an explanation of the stimulus 

 causing the formation of the gall it is necessar}' for us to turn our 

 attention to the mouthparts. 



For convenience the insects may now be divided into two 

 groups, those with mouthparts for sucking, which make their 

 attacks upon the outside, and those with mouthparts for biting, 

 which make their attacks from the inside. Under the former are 

 included the Acarina, the Hemiptera and the Diptera ; under the 

 latter are included the Lepidoptera and the Hymenoptera. 



I. HEMIPTERA. 



The Hemipterous insects which produce galls ma^- be placed in 

 the following order, with reference to the complexity of their 

 galls, beginning with the lowest : Schizoneura, Colopha, Horma- 

 ])his, Phylloxera, Pemphigus and Pachypsylla. Mouthparts of 

 the following were carefully examined : Schizoneura americana 

 Riley, Colopha ulmicola Fitch (Fig. 99), Hormaphis hamamelis 

 Fitch, Phylloxera carya-fallax Riley, P. c.-globuli WaLsli, P. 

 c.-spinosa Shinier, P. vastatrix Planchon, Pemphigus populi- 

 transversus Riley, P. p.-caulis Fitch, P. vagabundus Walsh, 



