a month: 
ILLUSTRATED J] 
PRINCIPALLY FOR THE NORTH 
fJRNAL 
iF ENG 
Edited by NVK ^ /£//? 
PEARSALL, D.Sc., F.L.S., andW>oR. GRIsf 
The University, Leed^>v^4, MusstJ 
with the assistance as referees in special depa TTiyioM . it . i 
Study in Variation : Pugnax Pugnus Martin and 
Pugnax cf. Sulcatus J. de C. Sow ( illustrated ) 
Brian Simpson, M.Sc. ( concluded ) . . . 73-77 
The Natural Abscission of Twigs in Canadian 
Black Poplar ( illustrated ) — Mary Thomas, B.Sc. 79-86 
The Great Crested Grebe Enquiry and Census of 
1931, in Yorkshire, and a few later notes — 
H. B. Booth, F.Z.S., M.B.O.U. 
Yorkshire Hemiptera During 1929-1932 — James M. 
Brown, B.Sc., F.L.S., F.E.S. . 
Reviews and Book Notices 
Field Notes 
News from the Magazines 
Illustrations 
LONDON : 
A. BROWN & SONS, Ltd., 5 Farringdon Avenue, E.C.4. 
And at Hull. 
Printers and Publishers to the Y.N.U. 
PRICE 1/6 net. 
Prepaid Subscription 
15 / - per annum. 
No. 915 
No. 688 of current Series 
RIL, 1933 
Professor A. Gilligan, D.Sc., F.G.S., M.I.M.E. 
F. A. Mason, F.R.M.S. 
Mrs. Elsie M. Morehouse, Mem. Brit. 
Conchol. Soc. 
Thos. Sheppard, M.Sc., F.G.S. 
T. W. Woodhead, Ph.D.,M.Sc., F.L.S. 
H.B. Booth, F.Z.S. M.B.O.U. 
J. M. Brown, B.Sc., F.L.S. , F.E.S. 
Chris. A. Cheetham, F.E.S. 
W. J. Fordham, M.R.C.S., L.R.C.P., 
D.P.H., F.E.S. 
Riley Fortune, F.Z.S. 
Contents 
