98 ' LOctobcr, 



larvae iu great abundance on tlie snowberry bushes in my garden. I 

 am not consequently in a position yet to say anything positive as to 

 the sex of the parthenogenetic brood. Most of the larvae, however, 

 attained fully the size of those last year from which I got nothing but 

 female flies. In the case of IV. rihesii, when the larva? are fed-up it is 

 easy to distinguish the males from the females by the difference of 

 size, the former being about f the length and i the bulk of the latter. 

 A similar and equally marked differentiation into two sizes was 

 observed among the full-fed larvae of Zarcea, but very few of the 

 smaller ones succeeded in making cocoons — many, indeed, of both sizes 

 perishing at this stage. 



The saw is of the usual S- or sabre-shape, with the distal con- 

 vexity looking ventrally or forwards. Each sheath is barred trans- 

 versely with lighter and darker (chitinous ?) lines. The saw" itself is 

 not entirely separable from its sheath, as figured by Eeaumur in the 

 case of other saw-flies ; but is connected with the sheath by short 

 (muscular ?) ligatures, running from the lighter (inter-chitiuous) bars 

 of the sheath to the back of the saw. The operation of making the 

 mine and depositing the egg, which occupies 1\ — 2 minutes, is very 

 easily witnessed, especially in the more transparent snowberry leaf, 

 with the aid of a lens. The fly sits on the edge of the leaf holding it 

 firm between the apical spines of the posterior tibiae. The ovipositor 

 being inserted under the epidermis is first thrust backwards, parallel 

 with the edge of the leaf, to its full extent, and then swept round till 

 it lies again under the edge of the leaf in front of the point of 

 insertion, which is situated rather behind the middle of the mine — the 

 saw all the while playing with short quick strokes, which gives it 

 somewhat the appearance of watchwork running down. The mine 

 so made has a shape or contour not unlike that of the human stomach, 

 the place of insei'tion (of the saw) corresponding to the cardiac 

 orifice of the stomach, and the anterior portion of the mine answer- 

 ing to the pyloric end of the viscus. The ovipositor is next brought 

 back to a position midway in the mine and at right angles to the 

 axis of the fly ; and after a short delay the egg descends between 

 the two blades with its long axis also at right angles to that of the 

 fly. The egg is green in coloiir, and in shape crescentic with the 

 horns rounded-off. AVhile it is between the blades of the ovipositor 

 the lowermost end (in advance) would correspond with what should 

 be the posterior or caudal end ; and the concave edge, looking for- 

 wards, with the ventral surface ; supposing its parts to have the same > 

 relations as the eggs of other insects. 13 at when the egg is escaping 



