144 



PROCEEDINGS. 



January 9th, 1885. — Conversational Meeting. 



The second of the third series of demonstrations was given this evening 

 by Mr. B. T. Lowne, P.R.C.S., F.L.S., &c, " On the Structure of the Eyes 

 of Arthropoda." 



After explaining the manner in which optical images are formed, Mr. 

 Lowne described the structure of the compound eye in insects, and gave a 

 resume of the mosaic theory of compound vision, as expounded in the classical 

 work of Johannes Midler. The lecturer pointed out the optical difficulties 

 resulting from this theory, as it is received by Grenacher and others, and 

 then proceeded to explain his own views. 



He regarded the whole of the great rods and the structures between them 

 and the cornea as dioptric in function. 



This view was founded on microscopical observations and physical con- 

 siderations. The chief new points he insisted upon were the existence of a 

 true bacillary layer, rods comparable with those of the vertebrate eye beneath 

 the great rods. These, with the optic nerve were, according to his obser- 

 vations, frequently separated from the optical portion of the eye by a con- 

 tinuous non-perforated membrane. The great rods consisted of tubes, 

 which the lecturer considered as very thick lenses of short focal length. He 

 stated that during life these tubes were filled with an oil-like fluid, which 

 escaped, leaving the empty, shrivelled tubes when the eye was injured ; 

 hence the very various appearances described by different authors. Accord- 

 ing to Mr. Lowne's view, the great rod magnifies and erects the sub-corneal 

 image, and has its posterior focus on a true retina comparable with that of 

 a vertebrate. In the course of the discussion which followed, the lecturer 

 stated that the nervous structures of the insect's eye are apparently de- 

 veloped, like the retina of a vertebrate, from the nervous ganglia as an out- 

 growth, whilst the optical structures, including the great rods, arise as a 

 modification of the sub-corneal epithelium ; and he explained the manner in 

 which the focal length of the lenses formed by the great rods could be cal- 

 culated, and the close correspondence of the actual and calculated distance 

 of the retina from the sub-corneal image. 



For further details Mr. Lowne referred his hearers to the " Trans. Linn. 

 Soc," Vol. ii., pt. 11., New Series 



The following objects were exhibited in the library : — 



Circulation in the egg of trout Mr. F. W. Andrew. 



Crenulated antenna of a moth, Pyq&ra bucephala, ),___. , 



' JJ l hMivF. Enock. 



retaining natural form and colour ... ... * 



Parasite of seal, //. strongly formes Mr. H. E. Freeman. 



Acants, sp Mr. W. Goodwin. 



Zoophytes, from Cape Good Hope Mr. J. D. Hardy. 



