5oin 3 
X 4 14°) 
SUMMARY 
This investigation was undertaken with the conviction that 
an intensive study of any group of species should contribute 
to the elucidation of biologic problems of general concern. 
Ninety-three species represented by more than 17,000 insects 
and 54,000 galls have been available for this analysis of the 
genus Cynips and these have offered an opportunity for study- 
ing the nature of species, individual variation, mutation and 
hybridization in nature, and the factors affecting the origin of 
species. 
Species are defined as populations with common heredity. 
The thesis is maintained that species, in this sense, are more 
than mental concepts — that species are realities which pre- 
serve a morphologic and physiologic identity under varying 
conditions, over vast areas, and thru periods of time that may 
extend beyond the present geologic epoch. Within these popu- 
lations individuals are found to vary, mutations to occur, and 
Mendelian races to develop as they are observed to develop in 
the laboratory. It appears that in Cynips, at least, these 
mutations have been the chief source of new species, but only 
when they are isolated from close relatives with which they 
might have interbred. Altho hybrid individuals prove com- 
mon, and local colonies which have arisen by hybridization 
between related species are not unknown, the isolation of such 
hybrid populations to form species seems to have occurred in 
only a few instances in this genus. 
The data on which these conclusions are based constitute 
a taxonomic revision of the genus Cynips. The group as re- 
defined is a homogeneous unit delimited by insect morphology, 
gall characters, host relationships, life histories, and geo- 
graphic distribution. Published records are coordinated with 
a large body of new data on these several aspects of the group. 
Of the 93 species placed in this genus, 45 have previously been 
described (only 26 of which have heretofore been recognized 
in Cynips) and 48 are new to science. To the 5 instances of 
alternation of generations which have previously been pub- 
lished for the group, 6 additional cases are added. 
It should be of some moment to correlate these conclusions, 
concerning the nature and the origin of the species of Cynips, 
with the studies that have been made or remain to be made 
on the evolution of other groups of organisms. 
( 5 ) 
