GALLS CAUSED BY SAW-FLIES 19 



ing that it was given them to enable us easily to observe 

 their marvellous operations. The sexes appear to be equal 

 in only a few species. As a rule, the females are far more 

 numerous than the males, and in some species males are 

 unknown, parthenogenesis being frequent, For details 

 concerning the habits of these most interesting insects the 

 reader should consult Cameron's "British Phytophagous 

 Hymenoptera," from which invaluable work I have taken 

 the following paragraphs concerning the gall -causing 

 species : 



" So far as my observations go, I do not find any marked 

 difference in the mode of oviposition of the gall and non- 

 gall-making saw-flies. I have noticed with some of the 

 latter incipient gall formation following oviposition. No 

 doubt the distinction between the two lies in the fact that 

 the former brings its eggs in contact with the cambium 

 layer, the latter not." 



" Unlike what happens with a cynips, the saw-fly gall is 

 fully formed before the larva leaves the egg, so it is clear 

 that the larva can have nothing to do in setting the gall 

 growth in motion ; while in the cynipidae no gall commences 

 to form until such time as the larva quits the egg and com- 

 mences to feed. The cynips larva, again, feeds on a 

 particular layer of the gall — namely, that part which im- 

 mediately surrounds itself, and which contains a large 

 quantity of starchy matter. They feed up also very rapidly. 

 The saw-fly larvae consume every part of the gall, which 

 does not contain a special layer of nutriment, all the gall 

 (except, perhaps, the outer skin) affording nourishment. 

 They do not either feed up in a few days, like most 

 cynipidae ; they are not, indeed, any more rapid feeders 

 than other larvae. In their general habits and mode of 

 forming the cocoon they do not differ from their congeners 

 which feed openly." 



" The structure of the saw-fly galls is, except in the case 

 of the woody galls of Euma pentandrae, very uniform. They 

 are composed of irregular cells, the ordinary cellular struc- 



