71 



one. Another species attacks the eyes of sufferers from ophthalmia in 

 Egypt. The malignant species are not believed to occur in Britain. The 

 paper was illustrated by lantern slides and microscopical preparations. 

 There was a short discussion, in which the Chairman, Messrs. Edgar E. 

 Waite, F.L.S., and Harold Wager took part. 



Meeting held in the Municipal Buildings, November 24th, 1890, 

 James W. Addyman, B.A., in the chair. 



THE SURFACE FILM OF WATER AND ITS RELATION TO PLANTS AND 

 ANIMALS. 



PROFESSOR L. C. MIALL, F.G.S., F.L.S. 



A number of interesting physical experiments were first made in proof 

 of the microscopical film upon water. Objects whose specific gravity are 

 heavier than water were placed on the top, and by the surface film floated, 

 but when the film is broken thi-ough the objects descended to the bottom. 

 It was shown that this surface film in relation to plants and animals was 

 full of interest to naturalists ; at the same time, it was a new subject, and 

 would well repay the personal observations of members. Attention was 

 directed to some intei-esting facts in water-lilies, the provision in nature 

 for the leaves and buds to cut the surface film. Each is provided with a 

 fine tapering point, which readily cuts the film ; the leaves then unfold, 

 and rest on the top of the water; if by chance the leaf become submerged, 

 the scoop-like leaf, with its sharp edge all round, cuts the film, and the 

 water runs oif through the slit adjacent to the stem. Without these 

 provisions these plants would have the greatest difficulty to get through 

 this elastic surface film. The duckweeds were next alluded to. It was 

 shown that the common oval leaf duckweed was able to cut the surface 

 film, and always gi-ows on the top of the water ; whereas the ivy-leaf duck- 

 weed, which cannot cut this film, was always found under water. Several 

 other plants were mentioned, which had each their peculiar way of coping 

 with this film. To a number of insects the svirface film formed a safe 

 platform to skate and jump upon. Their tarsus, or feet, are covered with 

 many hairs, which thus enable them to skim on the surface. Many 

 interesting facts were given in regard to dipterous larvie and the 

 water-spider. 



THE CONVERSAZIONE. 



The annual conversazione was held at the Philosophical Hall on 

 Wednesday evening, December 3rd, 1890. Cofl'ee was served at half-past 

 seven, and for half au hour a reception was held by the President 

 (Professor De Burgh Birch, M.D.). For the entertainment and instruction 

 of the guests abundant provision had been made. Those lightly affected 



