TO [March, 



" Jordan's " species — troublesome, no doubt, to systematists whose atten- 

 tion is confined to museum specimens, but not to be neglected on that 

 account by those who wish to study insects as living things. Single 

 examples without data may defy anyone to refer them with certainty to 

 either of the three categories, but in a gathering of moderate quantity 

 from Huhus, TIrtica, and Salix respectively the majority of specimens 

 will be found to exhibit the characters proper to their kind. 



In dealing with Jassids one finds that in most cases where there is 

 a colour- pattern distinctive of a jjarticular species, the percentage of 

 specimens exhibiting all the elements of that pattei-n is very small. 

 This circumstance has not hitherto received the attention which it 

 deserves, and the failure to appreciate it has led to much misapprehen- 

 sion as to the hmits of natural categories in these insects. It has been 

 shown in the case of some fungi that certain morphological characters 

 are due to food-factors ; and there is reason to believe that this is also 

 the case in some Cicadina, e. g. the ruM group of Macropsis ; the kinds 

 of Oncopsis living on alder, birch, hornbeam, and hazel respectively ; 

 Zygiiia coryli Toll., alneti Dahlb., and mali Edw. and so on. 



Colesborue, Cheltenham. 



February IQth, 1919. 



NOTES ON SAWFLIES {PTER0NV8 PINT AND PTERONUS SERTIFER). 

 BY T. A. CHAPMAN, M.D., F.E.S. 

 (Plates I-III.) 

 My acquaintance with these two species depends on material sup- 

 plied by Mr. E. E. G-reen, and still more is owing to the information he 

 has given me as to their habits, etc. He has also very kindly furnished 

 certain drawings, reproduced herewith. 



A first point of interest in these species is that Pferonus sertifer is 

 another sawfly that passes the winter as an Qgg. Perhaps the most 

 unusual habit that they have, is that instead of making room for their 

 eggs by pushing aside the tissues of the plant amongst which they are 

 laid, usually by elevating the cuticle, the space required for the eggs is 

 made by actually excavating the material from the area they will occupy. 



I do not know whether anything has been previously said about the 

 egg-laying of Pteronus sertifer, except in Mr. Green's recent report to 

 the Entomological Society,* but that of P.pini is, in a sense, well-known, 



* Proc. Ent. Soc, Lond. 1917, p. 1. 



