984 Dr. H. Adler’s Researches on 
which had received the name of Yeras terminalis. This 
second form includes winged males, and females either wing- 
less or furnished only with the rudiments of wings. In other 
respects the two generations do not differ much in the totality 
of their organization. 
In another species of the same group, Biorhiza renum, the 
differences of structure between the two generations are far 
more striking. This insect (the agamic generation) is 
wingless, 1°5 millim. long; its abdomen is sessile. Its an- 
tenne have thirteen joints, its labial palpi two, its maxillary 
palpi four. From its eggs, deposited on the adventitious buds 
of the trunk, branches, or twigs, emerge, at the end of May or 
middle of June, a Cynips known under the name of Trigonaspis 
crustalis, and which differs very much from the preceding. 
It is 4 millim. in length; the male and female are both pro- 
vided with very long wings. ‘The antenne of the male have 
fifteen joints, those of the female fourteen; the labial palpi 
have three joints, the maxillary five. The colour and the 
sculpture of the body are very different from what is seen 
in B. renum. The ovipositor has also quite a different 
structure. 
In the species of these four groups, the transformations of 
which we have just traced from the observations of M. Adler, 
there is a cycle formed of two generations more or less distinct 
one from the other—one of which is represented only by 
females laying by parthenogenesis, while the other exhibits both 
sexes. This alternation, although very much diffused amongst 
the Cynipidee, is not the general rule. There are some Aphi- 
lotrices which reproduce in a continuous way without any males 
appearing. ‘The four species in which M. Adler has observed 
this mode of reproduction emerge in April, and have only one 
generation, of which the period of development is a year. 
The galls which furnish food and shelter to the Cynipide 
during the greater part of their existence, as is known, 
vary considerably in form, colour, size, and situation. They 
furnish good characters for distinguishing species which are 
otherwise difficult to separate. 
It has been generally supposed that it is the puncture of 
the gall-flies, with the introduction into the wound of a secre- 
tion peculiar to the insect, which causes an irritation and, in 
consequence, an abnormal production of cellular tissue. On 
this hypothesis the differences between the galls are to be ex- 
plained by the variety of the substances produced in the 
glands of the insect and deposited in the tissue of the plant. 
M. Thomas, of Ohrdruf, who has examined a great number of 
galls of insects and Acari, had already called in question this 
