April, 1904 .] Galls and Insects Producing Them. 
127 
were found (Figs. 107, 108). A careful study of the mouth- 
parts lead me to consider No. 107 as a true gallmaker and No. 
108 as a parasite. The mouthparts of the one which I consider 
a true gallmaker were as strong as those of C. petiolicola (Fig. 
103). The mandibles of the parasite (108) were equally strong 
and showed what appeared to be rudimentary gland structures. 
Holcaspis globulus Fitch was the only bud (i. e., incipient 
stem gall, Part III, F'ig. 34) gall examined. In the young larvae 
the mouthparts are weak, but as the larvae approach maturity 
the mandibles become very strong (Fig. 109) and well fitted to 
cut the opening for the escape of the insect. However, the 
mouthparts were not so strong as in the case of C. petiolicola, but 
the gall of H. globulus is not so dense as the gall of C. petiolicola. 
The mouthparts of Nematus pomum Walsh (Fig. no) were 
very similar to those of the Cynipidae. I am not inclined to con- 
sider the apparently glandular-like structure observed in a few 
species of any great importance. They may be suctorial or they 
may be degenerate organs. I consider the stimulus as purely 
mechanical. The character of the gall may depend upon the 
location, which would result in difference in tension in different 
parts of the plant on which the gall may be located and also upon 
the laws of natural .selection, which will be considered in the latter 
part of this paper. 
It would be interesting to know the exact time that cell divi- 
sion begins in the formation of a gall, but it is very difficult to 
make satisfactory ob.servations upon this point. Adler has made 
succes.sful observations upon this stage in Neuroterus laviusculus 
and Biorhiza aptera. He says: “The moment the larva has 
broken through the egg covering and has for the first time 
wounded the surrounding cells with its delicate mandibles, a 
rapid growth begins. This goes on so quickly that while the 
posterior part of the larva is still within the covering a wall of 
like growth of cells has already arisen in front. This rapid cell 
increase can be easily explained because the irritation set up by 
the emerging larva is exerted upon highly formative cells which 
collectively possess everj' condition of growth. The cells which 
are primarily around the larva cannot be distinguished from the 
parenchymatous cells from which they proceed.’’ 
4. LEPIDOPTKRA. 
A careful study was made of the mouthparts of the Gelechia 
solidagiuis Fitch (Fig. iii)and upon an undetermined species 
found upon Rudbeckia laciniata (Part VI ). The mandibles are 
larger and much stronger than in any of the Hymenopterous 
gallmakers which I examined. The gall is also much stronger 
than any of the Hymenopterous galls whose larvae were studied. 
No glandular structures were observed. 
