28 THE FUNCTIONS OF A LOCAL NATURAL HISTORY SOCIETY. 
progeny of the Cynips of the oak-gall being something which is 
described as quite a different genus and species. There is already 
some evidence to support the last theory. Interesting instances 
of this form of development are the Phylloxera and Pemphigus, 
belonging to the Aphis group of the Hemiptera, and their transfor- 
mations. In these cases there are actually two forms of winged 
insects of the same species living on different plants. The gall 
caused by these insects produces an emigrant form like the summer 
broods of aphis, which gives birth to a true sexual progeny. The 
female of this progeny creeps into a crevice of the tree and dies 
there, the body protecting the solitary egg, which hatches in 
the spring and reproduces the original gall. Nearly all these 
hemipterous gall-makers of the elm and poplar require two 
different food plants to enable them to complete the cycle of 
life. 
There are many interesting questions connected with other 
species, the satisfactory solution of which would not only be most 
interesting to the observer himself, but would contribute a stone 
for the construction of the great temple of knowledge. 
In conclusion, a very few words on the special methods to be 
employed in the collection and examination of plant galls. To 
begin at the beginning, it is first necessary to examine plants and 
collect their galls, and then to breed the perfect insects from them, 
Now, this is not a matter of much labour. If the galls be collected 
fairly mature, all that is necessary is to put them, according to size, 
in glass capped boxes, or lamp glasses closed at each end by a cork, 
or, if not very mature, to put the end of the branch bearing the gall 
in damp sand, and cover with a bell glass and wait the course of 
events. I need hardly say that when gathered, or when fully 
mature, a careful description should be made of the external 
peculiarities of the gall, its section and structure, and the name of 
the plant on which it was formed. <A specimen of the gall should 
be carefully preserved by appropriate means, either by drying or 
by immersion in alcohol—the latter is the only method to adopt 
with soft galls. When the perfect insect has appeared, it should 
be killed and carded in the usual way, and its name determined 
