495 



is, in the pnsent phase of the science, insufficient. The dift'erence 

 must be explained morphologically. This explanation is afforded by 

 the different modes in which the vertebrate and invertebrate, that is, 

 the simple and compound eyes are developed. 



In the compound eye the primordial ocular papilla or convexity, 

 which is only slightly protuberant, has its cutaneous or superficial 

 surface immediately converted into the crystalline columnar struc- 

 ture, the individual columns of which are connected with the fila- 

 ments of the subjacent optic nerve. The columns are all therefore 

 directed to the object. 



The primordial cerebro-cutaneous spheroidal protuberance or pa- 

 pilla of the simple refracting or vertebrate eye, is speedily hollowed 

 out in front by the development in or upon it of the lens and vi- 

 treous humour, so that from a spheroidal convex surface the pri- 

 mordial protuberance assumes the form of a cup, with its mouth di- 

 rected forwards, and its cavity occupied by the refracting media of 

 the organ. This cup-shaped mass is the retina ; the crystalline rods 

 are not developed on its concave surface, but on its outer or convex 

 surface, as they exist on the convexity of the compound eye, that is, 

 in the direction of the radii of the sphere, but directed backwards, 

 on account of the nearly spheroidal surface. 



In conclusion, I may state, what appears to be the physiological 

 superiority of the simple over the compound eye. As the simple eye 

 is acted on by reflected light only, it cannot be disturbed by rays 

 not required for the definition of the image. It is also arranged so 

 as to admit of a much more delicate or minute mosaic representa- 

 tion of the object, from its microscopic and reversed photaesthetic 

 bodies being in contact with the reflecting choroidal surface on which 

 that image is formed. It moreover combines the advantages of the 

 continuous image, formed by the lenticular structures and the mosaic 

 image, which results from its crystalline rods. 



The following Gentleman was admitted an Ordinary Fel- 

 low : — 



Thomas Login, Esq., Civil Engineer, India. 



The following Donations to the Library were announced : — 



Monthly Return of the Births, Deaths, and Marriages, registered 

 in the eight principal towns of Scotland, with the causes of 



