GALLS FOUND NEAR BOSTON. 63 



development of the down usuall}- to be found on young oak leaves. 

 Mr. Bassett, of Waterbury, Conn., has discovered that in the 

 woolly gall of Cynips seminator on the white oak, the hard kernel 

 answers to the leaf-stalk, and the long wool is an enormous devel- 

 opment of the down of the leaf. 



These hairs are supposed to be of service to the gall in prevent- 

 ing the attacks of parasites. The liabilit}' of galls to the attacks 

 of these parasites often renders it difficult to rear the true gall 

 maker, and the parasites sometimes so closely resembles the true 

 gall makers that one not an entomologist cannot distinguish them. 



If, before an oak gall is fully grown, its larva is attacked by a 

 parasite, the gall never assumes its perfect shape, the life of the 

 larva being a necessar}' factor in its development. But many 

 perfectly formed galls also produce parasites, which I suppose 

 did not attack them till the larva had completed its gi'owth. 



Besides being subject to the attacks of these enemies, some 

 galls harbor what are called "guest insects," which live vnthin 

 the gall substance but in no way disturb or incommode the true 

 gall maker. 



The larvae of these oak gall insects, are white, or whitish, with 

 an inconspicuous head and no legs. The body is more or less 

 cylindrical, tapering at each end, and lies in a curved position 

 within the cell. The larvae change to perfect insects within the 

 cells, and the gall-flies finally emerge, leaving the gall pierced 

 ■with one or many holes, according as it contained one or many 

 cells. 



The perfect gall-flies are usually quite small. But, small as 

 they are, entomologists have put them under their microscopes, 

 and studied their minutest details of structure, and found them 

 to be so different from each other that they have divided them 

 into different genera, and whereas they used to be all called 

 Cynips, now some of them are named Callirhytis, some Neuroterus, 

 others Andricus, Biorhiza, etc. 



The ovipositor, or apparatus which the little creature has for 

 piercing the plant tissues and laying its eggs, is quite complicated, 

 and consists of two plates which form a kind of sheath, and a 

 piercer, composed of three pieces, one stout and deeply grooved 

 longitudinally, and two others, which are hair-like, and work 

 within this channel, beyond which they can be protruded when in 

 use. 



