1919.] 59 



though the only description o£ it I can find is b}^ a German author, and 

 is erroneous in the most important particular. 



As regards the actual egg-laying, I was unfortunate in never suc- 

 ceeding in seeing the actual process. AVith many of these sawflies, 

 e. g. species of Trichiosoma, Gimbex, Rhadinoceraea, etc., as soon as a 

 suitable piece of the food-plant is offered to a $ fly, she, practically 

 at once, proceeds to egg-laying, and there is no difficulty in observing 

 the process ; but with neither P. |;/«? nor sertifer did anything of this 

 kind occur. I kept watch for considerable periods, both immediately 

 after placing the flies on the j^lant and subsequently, but never saw any 

 attempt at egg-laying. Possibly this occurs most usually during dark- 

 ness. I once, however, found a $ of P. sertifer that had just completed 

 laying an egg. This was my nearest approach to success. 



When we examine a fir needle in which P. pini has laid eggs, we 

 find a considerable length of one margin has a covering of greyish-green 

 material. The extent of this may be gathered from Plate III, fig. 1, 

 which is a magnified stereoscopic view of such a pine leaf or needle. 

 Such a leaf is, of course, very obvious amongst its fellows. 



The German account of this structure regards it as consisting 

 of material supplied by the sawfly and describes the e^^ as being 

 covered by it, but as itself lying outside the substance of the leaf. 

 This is not so ; the egg is in the substance of the leaf, and the added 

 material consists of the particles excavated to make room for the eggs, 

 Avith almost certainly some agglutinating matter supplied by the 

 sawfly. The arrangement of this material is very regular and elabomte, 

 and may be understood by examining the drawings by Mr. Green on 

 Plate I and the photographs on Plate II. 



Mr. Green makes the following observations on the needles of pine 

 with eggs of P. pini : — " I think that you are correct in considering 

 that the lateral ridges are composed of secretionary matter — small 

 vacuoles or bubbles can be distinctly observed in the material. You 

 note that * these side lines are divided into portions corresponding to the 

 eggs.' My examination showed me that the median ridge is similarly 

 divided ; its divisions are slightly behind those of the lateral ridges, so 

 that they have the appearance of being * en echelon.'' Moreover, the 

 anterior extremity of each division (of the median ridge) is carried for- 

 wards and sideways to meet the corresponding sections of the lateral 

 ridges on each side. On Plate I rough sketches are given of the arrange- 

 ment, as I see it. The lower di'awing, fig. 2, is, of course, diagrammatic 

 and Is intended to represent the arrangement as vicAved from above. 



