78 INSECTS 



under the term Cynipoidca. These gall- wasps produce 

 in the plants attacked abnormal swellmgs or growths 

 known as galls, which are constant for every species 

 and differ as the species differ. Thus for those forms 

 whose life history is known, the gall is as good an index 

 to its kind as a specimen of the wasp. And the re- 

 markable point is, that the gall is purely a production 

 of the plant and the insect has, apparently, nothing 

 at all to do with it. The female lays the egg and in 

 due time a minute larva hatches. Immediately there 

 begins to develop around this larva an abnormal growth 

 centered by a smooth cell in which the larva lies, a 

 white helpless grub, feeding upon the exudations that 

 come from the inner side of the cell. The relation be- 

 tween the irritation set up by the minute larva just 

 out of the egg and the remarkably complicated struct- 

 ure of plant cells built up around it has never been 

 clearly elucidated and offers an excellent opportunity 

 for research. Some galls are spongy in texture, some 

 are solid; some are filled with radiating fibres extend- 

 ing from the central cell to the covering sphere; some 

 are no larger than necessary to accommodate the insect 

 and yet others are huge bladder-like affairs, out of all 

 proportion to the size of the larva. Some galls are on 

 leaves, some on twigs and branches and a few are on 

 roots. On the roots and stems the growths are often 

 corky or woody, and sometimes mere enlargements 

 of the normal growth. More generally the galls are 

 unicellular, i.e., they have only a single central cell 

 containing one larva; but very often also they are 

 multicellular, a large growth containing many larval 

 cells which, in turn, may be very regularly or very 

 irregularly disposed in the larger mass. 



These gall-wasps have a number of very interesting 

 features. Some of them appear, year after year, males 



