GALLS CAUSED BY GALL-WASPS 
3 1 
the genus Neuvoterus , arriving at the surprising result that 
from the eggs laid by these, wasps were produced which 
were so unlike their parents that they had been placed in a 
separate genus, Spathegaster. He published this fact in 
1877, and afterwards extended his observations to the 
majority of the Oak gall-flies of North Germany, showing 
that the phenomenon is observable in many species. 
Particulars concerning the methods of investigation 
employed by Dr. Adler in the course of his researches may 
be consulted in the first chapter of “ Alternating Genera¬ 
tions.” Oak saplings were used, either grown in pots 
or obtained from nurserymen ; those from four to six years 
old proved to be the most convenient size. It was found 
that gauze covers with a glass top were better than ordinary 
bell-glass protectors, the absence of free ventilation causing 
the latter quickly to become dimmed with moisture. It 
was easy to make experiments with species which prick 
the leaves or bark, but some difficulty was experienced 
with those which only prick flower-buds, as the majority of 
four to six year saplings do not produce catkins. Conse¬ 
quently the experiments were made in the open air on full- 
grown trees, using cubes of wire covered with muslin, and 
tied round the branch. “ It is an essential that a sapling 
about to be used in an experiment should have its buds 
well developed, as these are always preferred by the flies.” 
The following tables concern the known British species 
of gall-causing Cynipidae. If the second is examined in 
connexion with the footnote, it will be observed (omitting 
Cynips Kollavi and C. calicis for obvious reasons) that there 
are six species in which the agamous generation alone is 
known, and six in which it is unknown. It is probable 
that future research will show there are but six species, each 
with an alternating generation. 
