PROCEEDINGS OF SOCIETIES. 43 



little scollop, but how far this effect might be due to upstanding 

 spines or to beading was not quite clear. 



Mr. Slack observed that his remarks did not refer so much to the 

 edge of the hole as to the circumstance that the top of the framework 

 of the hexagon was composed of two or more rows of beads. 



Mr. Weiiham said there was one question as to an optical effect 

 which he thought might be easily settled. It was stated that an 

 aperture in the centre gave rise to what was known as an "eye spot." 

 This could be decided by experiment without difficulty by mounting a 

 piece of tin-foil upon glass, and pricking a hole in it with the point of 

 a needle, when the same effect ought to be produced. The conditions 

 might be altered in a number of ways, by making the holes of different 

 sizes, or mounting the tin-foil on the other side of the glass or in 

 different media. They had generally regarded the " eye spot " as 

 being produced by a membrane, but the question might easily be 

 settled, and he would endeavour to try it and give them the results. 



Mr. Charles Stewart thought it could be tried in many ways. A 

 large number of the silicious shells of PolycistinsB as well as the plates 

 of the Echinoderms undoubtedly had holes through them, and in all 

 cases they showed a very distinct image. The peciiliarity in the 

 instance before them was that it gave a positive image in all cases. 



Mr. Stephenson sup^wsed that nobody would deny that the Poly- 

 cistinfe had foramina. The formation of an image seemed to him to 

 be the same in principle as the formation of one in the well-known 

 camera-obscura experiment by making a hole through an ordinary 

 window-shutter, when objects outside were shown on a screen ; the 

 formation of the image of the sun when shining through the leaves of 

 trees was another case in point. 



Dr. W. J. Gray, in reply to a question from Mr. Slack, said he had 

 observed that there was a covering over the hexagonal framework in 

 Triceratium, but it did not follow that therefore the same existed in 

 Coscinodiscus. 



The President said that the formation of an image through an 

 aperture was a necessary consequence, but it shoidd also be borne in 

 mind that an image of that kind necessitated a screen upon which to 

 show it. 



Mr. Wenham said he was glad to see that Mr. Stephenson had 

 given in his paper the actual angular apertures in each instance. No 

 doubt an image was always formed by rays of light in passing through 

 a small hole, but it remained to be seen what effect lenses would have 

 upon such an image formed without lenses. 



The President gave notice that the library and reading room 

 would be closed during the month of August, and wishing the Fellows 

 a happy long vacation, the meeting was adjourned to October 1st. 



Eichard Branwell, Esq., M.E.C.S.L., was elected a Fellow of the 

 Society. 



Walter W. Eeeves, 



Assist. -Secretary. 



