The Ohio Naturalist. 
[Vol. II, No. 7 , 
270 
in its development before the separation of the two zones and the 
nourishment remaining in the inner zone at the time of the separ- 
ation is sufficient to complete its development. 
Adler and Stratton after describing similar modifications in the 
European Cynipidae galls, say: “Besides these histological 
differences, the outward characters are also of varying complex- 
ity ; each infinitesimal improvement, which has been of service 
as a protection against parasites, or has been successful in secur- 
ing natural conditions favorable to the life and growth of the 
larva, has been preserved, and has formed the starting point of 
further beneficial variation. It is always that larva which has 
been able to induce successful morphological abnormalitiou, which 
is reproduced to continue the race ; the unsuccessful perish. The 
ruling force is natural selection ; it is impossible that intelligence 
or memory can be of any use in guiding the Cynipidae ; no 
Cynips ever sees its young, and none ever pricks a bud the sec- 
ond season, or lives to know the results that follow the act. 
Natural selection alone has preserved an impulse which is released 
by seasonally recurring feelings, sights, or smells,* and by the 
simultaneus ripening of the eggs within the fly. These set the 
whole physiological apparatus in motion, and secure the insertion 
of eggs at the right time and in the right place. The number of 
eggs is instinctively proportionate to the space suitable for ovipo- 
sition, to the size of the fully grown galls, and to the food sup- 
plies available for their nutrition.’’ 
CONCLUSIONS. 
1. Galls may be classified into two general groups, viz., those 
produced by mouth parts and those produced by oviposition. 
Those produced by oviposition may be considered the more highly 
developed. 
2. The family Cynipidae shows by far the highest develop- 
ment of gall structures. 
3. The morphological character of the gall depends upon the 
genus of the insect producing it rather than upon the plant on 
which it is produced ; i. e . , galls produced by insects of a partic- 
ular genus show great similarity of structure even though on 
plants widely separated ; while galls on a particular genus of 
plants and produced by insects of different genera show great 
differences. This seems to indicate that the stimulus of a partic- 
ular genus of insect is given to a particular part of the host plant 
or is of a peculiar kind, characteristic of that genus. However, 
if the stimulus of two different genera of insects be applied to the 
same part of the plant the results may be similar. (See Part II. ) 
4. Within each family w r e find certain morphological resem- 
blances ; e. g . , Aphididae. 
Weismann, Essays on Heredity, Vol. I, p. 95. 
