186 THE GROUP OP GALL MAKERS. 



such time as the larva quits the egg and commences 

 to feed. The Oynips larva again feeds on a particular 

 layer of the gall, namely, that part which immediately 

 surrounds itself and which contains a large quantity 

 of starchy matter ; they feed up also very rapidly. The 

 sawfly gall larvas consume every part of the gall, which 

 does not contain a special layer of nutriment, all the 

 gall (except perhaps the outer skin) affording nourish- 

 ment. They do not either feed up in a few days like 

 most Cynipidce ; 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 sawfly galls is, except in the 

 case of the woody galls of Euura pentandrce, very 

 uniform. They are composed of irregular cells, the 

 ordinary cellular structure of the plant profoundly 

 modified. The cells forming the boundary are more 

 regular than those near the centre; they are also 

 smaller and more elongated; and this outer layer 

 (which may be composed of one, two, or three rows of 

 cells), contains few or no stomata. In the case of the 

 gall of N. gallicola, the cells adjacent to the epidermal 

 layer are filled with chlorophyl granules, which give to 

 this part a green granular appearance. Near the centre 

 the cells are paler, more irregular, contain apparently 

 less chlorophyl and more intercellular spaces. 



When the galls are young the cells are not at all so 

 irregular as they are later on, in fact at first they do 

 not differ much from the ordinary cells of the leaf. 



The gall of Euura pentandrce is much more com- 

 plicated in structure. Besides the outer bark layer 

 there is next to it a wide layer of cellular tissue before 

 the layer of woody fibre is reached; this, again, is 

 succeeded by the spongy mass representing the medul- 

 lary layer, on which the larvse feed. 



