264 THE entomologist's record. 



the prevalence of the best — manifests itself with equal distinctness, and 

 plays an ecjually essential part in the internal relations of the organism 

 in the great science which treats of them — physiology." 



That the oecological view of entomology is rapidly becoming the 

 most attractive none can donbt. The physiological still attracts, and 

 always will attract, many adherents, but the morphological (in its 

 superficial sense) is probably being played out. A certain level has 

 been reached in morphological entomology at which the superficial 

 structures of organs have been used to build up more or less artificial 

 systems of classification, which the continued observation of the last half 

 century has done little to solidify, and which are continuallj^ being upset 

 by everyone who approaches the subject on the physiological side. 

 That the oecological branch of the subject should, on such good 

 authority, be considered that in which " those qualities of mind which 

 especially distinguish the naturalist find their highest exercise," is a 

 circumstance which should encourage those who engage in its studj^ 

 even though they sometimes be vaguely classed as dreamers and 

 theorists by men who are unable to see any good in philosophical stud3> 

 observation, or speculation. 



There is, towards the end of the President's address, a direct refer- 

 ence to our favourite study. It relates to vision in insects and the 

 action of the compound eye in forming the picture which is transmitted 

 to the optic nerve centre. He says : — " Let me conclude with one 

 more instance of a different kind, which may serve to show how, 

 perhaps, the wonderful ingenuity of contrivance which is displayed in 

 certain organised structures — the eye, the ear, or the organ of voice — 

 may be of no less interest to the physicist than to the physiologist. 

 Johannes Miiller, as is well known, explained the com2)ound eye of 

 insects on the theory that an erect picture is formed on the convex 

 retina bj^ the combination of pencils of light, received from different 

 parts of the visual field through the eyelids (ommatidia), directed to 

 them. Years afterwai'ds it was shown that in each eyelet an image is 

 formed which is reversed. Consequently, the mosaic theory of Miiller 

 was for a long period discredited on the ground that an erect jjicture 

 could not be made of " upside-down " images. Lately the subject has 

 been reinvestigated, with the result that the mosaic theory has regained 

 its authority. Professor Exner has proved, photogTaphicall}', that 

 behind each part of the insect's eye an erect picture is formed of the 

 objects towards which it is directed. There is, therefore, no longer 

 any difficulty in understanding how the whole field of vision is mapped 

 out as consistently as it is imaged on our own retina, with the differ- 

 ence, of course, that the j^icture is erect. But behind this fact lies a 

 physical (piestion — that of the relation between the erect pictixre which 

 is photographed, and the optical structure of the crj^stal cones which 

 produce it — a question which, although we cannot now enter upon it, 

 is quite as interesting as the physiological one." 



" With tills history of a theory'- which, after having been for thirty 

 years disbelieved, has been reinstated by the fortunate combination of 

 methods derived from the two sciences I will conclude. It may serve 

 to show how, though physiology can never become a part of natural 

 philosophy, the (questions we have to deal Avith are cognate. Without 

 forgetting that ever}'^ phenomenon has to be regarded with reference 

 to its iiseful purpose in the organism, the aim of the ph^'siologist is not 



