404 
Indiana University Studies 
Five pages of Triggerson’s paper are given to the life history 
of the gall maker, and another five pages to the parasites and 
inquilines. The remaining fourteen pages are given to an in- 
teresting if unconvincing discussion of the stimulus to gall 
production. Following a suggestion of Rossig’s (1904), Trig- 
gerson studied the Malpighian tubules of erinacei and con- 
cluded that they “secrete a fluid which stimulates the plant to 
produce the gall.” He summarizes his reasons for so believing 
as follows: 
A. The character of the Malpighian vessels of the sexual and 
agamic forms of Dryophanta erinacei — their size, cellular structure, and 
exceptional glandular activity. 
B. The character and effect of the secretion poured forth by the 
Malpighian vessels during gall formation. 
C. The ultimate decline and ceasing of marked activity of the 
tubules when the gall has matured. 
D. The increase in the size of the cells of the Malpighian vessels 
coincident with the development of the gall, and their decrease in size 
when the demand upon them is withdrawn. 
E. A comparison of the Malpighian vessels of Dryophanta erinacei 
with those of the parasites and the inquilines found in the gall, and 
particularly the lack of any abnormal secreting activity in the latter. 
F. A study of the Malpighian vessels of Holcaspis globulus, and 
Dryophanta polita, both of which correspond in their action, develop- 
ment, and degeneration to those of Dryophanta erinacei. 
G. A comparative study of the Malpighian vessels of Dryophanta 
erinacei with those of Nematus pomum, Trypeta solidaginis, and Ceci- 
domyia strobiloides shows that all the latter, though gall producers, 
possess tubules of normal type, which do not pour forth an abundant 
secretion during gall development, nor when in contact with foreign 
substances. 
H. The study of the Malpighian vessels of species of Braconids 
and Ichneumons, shows tubules with cells not larger than those of the 
Chalcids and inquilines. The mode of degeneration however, appears 
similar to that found in Dryophanta erinacei. 
While I do not believe that Triggerson’s data fully support 
the conclusion on the gall making stimulus, this paper should 
be carefully weighed by some future investigator whose studies 
will include a wider selection of gall wasps. Convincing proof 
of the source of the stimulus must include the artificial pro- 
duction of a specialized gall, or at least the control of gall 
production by the control of the suspected gall producing struc- 
tures of the larval cynipid. Further discussion of this ques- 
