442 SECTIONAL TRANSACTIONS— D. 



Experimental data show that the formation of the gregarious phase from 

 the solitary occurs as a direct result of crowding hoppers into a limited 

 space. This transformation is brought about by the increased activity due 

 to mutual stimulation. 



Attempts are made to analyse in the light of recent research the factors 

 involved in this crowding and thence to determine why the phases take on 

 their particular characters. 



Afternoon. 



Semi-popular Lecture by Mr. H. C. Gilson on Lake Titicaca (2.15). 



An expedition financed by the Percy Sladen Trust left England in March 

 1937 to spend six months from April to September studying the conditions 

 of life and the fauna and flora of Lake Titicaca and other bodies of water in 

 its neighbourhood. Lake Titicaca is a tectonic lake some 100 miles long 

 by 30 wide and about i ,000 ft. deep at the deepest. It lies in latitude 16° S. 

 at an altitude of 12,500 ft. above the sea, on the high central plateau of the 

 Andes, some two-thirds of its area being in Peru and the rest in Bolivia. 

 It is an area of inland drainage which has probably been isolated from other 

 water masses since the Eocene period, and it was already known from the 

 work of other expeditions to have a somewhat peculiar fauna. This proved 

 to be rich in individuals but poor in species, making it a very interesting 

 study for the ecologist. 



An account illustrated by lantern slides and cinematograph film is given 

 of the life and work of the expedition and of the native ' Indians,' who are 

 the descendants of the people of the Inca regime. 



Exhibition of biological films (3.15). 



Films produced by Strand Film Co., Ltd., under the direction of 

 Dr. J. S. Huxley, F.R.S, :— 



Fitigers and thumbs. 

 Monkey into man. 



Films produced by Gaumont-British Instructional Films Co., under 

 the direction of Mr. H. R. Hewer : — 



The Lwerfluke. 



The Crayfish. 



The development of the Trout. 



Tuesday, August 23. 



Symposium on The rSle of the environment in animal locomotion (lo.o). 

 Prof. J. Gray, F.R.S. — Introduction. 

 Mr. J. E. Harris. — Aquatic forms ('10.15). 



Prof. J. Gray, F.R.S., and Dr. Lissmann. — Terrestrial forms (10.45). 

 Dr. F. S. J. HoLLiCK. — Aerial forms — insect flight {11. i^). 

 Dr. C. Horton-Smith. — Aerial forms — bird flight (11.45). 

 Discussion (12.15). 



