I 22 
The Ohio Naturalist. 
[Vo]. IV, No. 6, 
OVIPO.SITORS. 
Gall-making insects deposit their eggs b}' two methods, either 
on the surface of the plant or within the tissues. Those insects 
which deposit their eggs on the surface usually have mouthparts 
developed for sucking, while those which deposit their eggs 
within the tissues usuall}’ have mouthparts developed for biting. 
Those which deposit their eggs on the surface of the plant are 
the Acarina, the Hemiptera, and the Diptera. Those which 
depo.sit their eggs within the tissues are the Hymenoptera and the 
Lepidoptera. In this paper we have made a careful stud}’ of the 
ovipositors of Cecidomyia gleditsiae, of Nematus .sp , Dr}-- 
ophanta palustris, Amphibolips radicola, Andricus cornigerous, 
A. seminator, and Rhodites radicum. A number of others were 
examined, but because of the uncertainty as to determination are 
not figured. 
The Cecidoni3'ia ovipositor (Fig. 92) is not .suited to punctur- 
ing tissues. The gall is never formed until after the hatching of 
the larva. In this case it is evident that the stimulus, whether 
mechanical or chemical, is produced by the larva. 
Insects belonging to the genus Nematus deposit their eggs 
either on the surface of the plant or in .slits made by the ovipositor 
(Figs. 93a, b). It is said that the galls are formed from these 
wounds before the larva escapes from the egg, and in the.se cases 
it is claimed that the irritating cause is a drop of fluid secreted 
by the parent in.sect. \Ve.stwood claims that the egg increa.sing 
in size is a result of imbibing sap from the wound in the plant. 
It is well known that the eggs of .some insects increase in .size as 
a result of the growth of the embryo within the egg. I have so 
far been unable to make any .satisfactory observations upon the 
Nematus galls, but it is probable that the eggs increa.se in size 
from the growth of the embryos and not as a result of the absorp- 
tion of plant sap. It is also possible that the gall may be the 
result of the mechanical irritation of the ovipositor or the enlarge- 
ment of the egg or both. The wound cau.sed by the ovipositor 
of the Nematus is very much more severe than the wounds caused 
by the ovipositors of the Cynipidous imsects. 
Adler, after a careful observation on Nematus \hillisnierii, says: 
“This fly, which is armed with a finely serrated terebra, cuts 
into the tender leaves of the end of the shoot of the Salix amyg- 
dalina, and inserts her egg into the open wound, frequently plac- 
ing several in the same leaf. At the .same time the glandular 
secretion flows into the wounded leaf. A few hours after this 
injury the leaf surface presents an altered aj)pearance, and new 
cell formation begins freely, leading to a thickening of the sur- 
rounding leaf surface. After the lapse of about fourteen days 
tlie green and red-shaped gall is fully grown. If it be now 
