124 
The Ohio Naturalist. 
[Vol. IV, No. 6, 
O. S., Holcaspis centricola O. S. , Dryophauta jjalustris O. S., 
and Callirli3-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 necessar}* to penetrate a stem. Adler’s 
obser\’ations demonstrate that great force is used to penetrate the 
buds and reach the desired point for depositing the eggs. 
Bej'erinck has demonstrated that the fluid ejected by the ovi- 
positor of the Cynipidae is v’erj’’ 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 ma}" 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 
uide.ss it ma}^ 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, saj’s, in regard to Trigonaspis : “ This flj’ pricks 
the leaf in May, but months pass before an\" 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 in.serted. Guided b>- these 
marks it is eas>" to And 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 
cau-sing the formation of the gall it is necessar}" for us to turn our 
attention to the mouthparts. 
For convenience the insects inaj' 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 Ilemiptera and the Diptera ; under the 
latter are included the Lepidoptera and the Hymenoptera. 
I. HEMIPTERA. 
The Hemipterous insects which produce galls may be placed in 
the following order, with reference to the comi^lexit}’ of their 
galls, beginning with the lowest : Schizoneura, Colopha, Horma- 
phis. Phylloxera, Pemphigus and Pachypsylla. Mouthparts of 
the follow'ing were carefullj- examined : Schizoneura americana 
Riley, Colopha uhnicola Fitch ( Fig. 99), Hormaphis hamamelis 
Fitch, Phjdloxera carjm-fallax Riley, P. c.-globuli Walsh, P. 
c.-spinosa Shinier, P. vastatrix Planchon, Pemphigus populi- 
transversus Riley, P. p.-caulis Fitch, P. vagabundus Walsh, 
