Fordham : Yorkshire Coleoptera in 1917. 135 



this, or that if the Gull had acquired a contempt for the Peewit, 

 the Peewit, at any rate, must look with terror and resentment 

 on the Gull. But if this last is the case, how is it that the 

 two birds may constantly be seen standing almost side by side, 

 with apparent indifference, and that, until the actual chase 

 is begun, the Peewit never seems at all afraid of its persecutor. 

 And then, too, an instinct would seem to have been developed 

 in the Gull similar to that which restrains a shepherd's dog 

 from biting the sheep, and only allows him to drive and hustle 

 them. Though he pursues closely, he does not actually attack, 

 and his very cries seem to express complaint, rather than anger, 

 as though he were demanding what the Peewit, as well as 

 himself, knew to be his due. It is at least possible that this 

 may really be the case. However a habit of this kind may 

 have commenced, when once the weaker bird had come to be 

 terrorised by the stronger one, the latter would be likely, on 

 the principle of ' least action,' gradually to accustom itself to 

 threaten only, and the threat, in time, would be responded to 

 more as an instinct than in fear of something that had ceased. 

 Thus, to the Gull, the Peewit might become by degrees first 

 a subject having duties, and at last a dutiful subject ; whilst 

 the Peewit would see, in the Gull, not so much an oppressor 

 as an existing necessary state of things — in fact, an institution 

 which would make it all right. This curious result to which our 

 human experience may offer, here and there, some analogy, 

 is perhaps the most interesting feature in a species of parasitism 

 which is in itself full of interest. Indeed, we might almost 

 call it commensalism, since the sooner the Peewit gives up 

 what it has, the sooner it can get something else, which is 

 gain too — of a sort. 



YORKSHIRE COLEOPTERA IN 1917. 



W. J. FORDHAM, M.R.C.S., L.R.C.P., F.E.S. 



{Continued froyn page 102). 



Aihous vittatus F. Roundhay Park, 6-16. S. D. F. Colhng- 



ham, 6-16. E. C. H. *64. Escrick, 6-17. W. J. F. *6i. 

 Trixas;us ( Throscus) dermestoides L. Collingham, 6-16. 



J. D. F. *64. 

 Helodes marginata F. Morton Wood, Hepworth. Several. 



Lower Harden Clough, Meltham, 7-17. W. Falconer. *63. 

 Scirtes hemisphericus L. Menthorpe Ings. One, 26-6-17, 



by sweeping. Extremely abundant on Sallows, 28-7-17. 



W. J. F. *6t. 

 Podabrus alpinus Pk. Martin Beck Wood. H. H. C. 

 Cantharis bicolor Hbst. {thoracica 01.). Menthorpe Ings. 



Several. 7-17. W. J. F. 



1918 April 1. 



