SECTIONAL TRANSACTIONS.— D. 331 



Dr. R. Lawrence. — The Lung-books of the Scorpion. 



Mr. J. S. VAN DER LiNGEN. — HolothuHan Hoemoglobin. 



Mr. L. MiRViSH. — The Nervous Control of Colour Response in the Chameleon. 



Miss Russell. — Fertilisation Phenomena in the Cape Sea-urchin. 



Mr. D. Slome. — The Chromatic Response in Xenopus. 



Miss Starke. — Chromosomes and Cell-inclusions in Holopterna. 



Mr. A. ZooND. — The Octopus Heart. 



Dr. J. H. Ferguson. — Ultra-microscopic Examination of ' Surviving 

 Blood.' 



Thursday, July 25. 

 Joint Discussion with Sections I {q.v.) and K on The Nature of Life. 



Afternoon. 

 Excursion to Table Mountain. 



Friday, July 26. 



Dr. F. A. DixEY. — South African Lepidoptera in their relation to conditions 

 of Climate and Vegetation. 



The lepidopterous fauna of South Africa is influenced in its character and distribu- 

 tion by the physical conditions of the subcontinent ; chief among •which are the 

 configuration and elevation of the land, the action of oceanic currents, the direction 

 of the winds and the incidence of the rainfall. These influences act upon the fauna 

 largely through their effect on the vegetation ; partly also by a more direct control. 



The general land surface rises in a succession of plateaux from sea-level to an 

 elevation of over 5,000 feet ; the comparative poverty in natural vegetation of the 

 uplands of the interior is accompanied by a corresponding scarcity of lepidopterous 

 insects. The contrast between the west and east coastal regions is a marked one ; 

 the former, under the influence of the cold antarctic current, shows at corresponding 

 latitudes a considerably lower average temperature than the eastern coast belt, which 

 is washed by the warm water of the Mozambique current of the Indian Ocean. A further 

 difference between west and east is afforded by the rainfall. Over a large portion of 

 South-west Africa the rainfall is extremely scanty ; at Walfisch Bay the annual 

 average is under 1 inch. The amount generally increases as one goes eastward, being 

 about 40 inches in Zululand. These differences of warmth and moisture have, 

 naturally, a great effect on the vegetation and so on the wealth of insect Ufe. The 

 conditions on a large part of the eastern coast belt are subtropical, and from East 

 London northwards the comparative abundance of lepidoptera, especially of butter- 

 flies, is very noticeable. 



It is well known that in the western districts of the Cape Province the rain falls 

 mostly in the winter ; in other parts of South Africa the rainy season, if anj', is in the 

 summer months. This is due to the position in winter and summer respectively of 

 anticyclonic centres, and the consequent course of the accompanying winds over sea 

 or land before reaching a given area. Seasonal range in South Africa affects lepidop- 

 tera chiefly by alternation of wet and dry rather than of hot and cold conditions. The 

 seasonal phases shown by many of tlie butterflies, especially Pierinae and some 

 Nymphalinae are particularly well marked. They appear to be dependent partly on 

 alternate abundance or scarcity of vegetation, partly on other causes, especialh'^ on 

 the means of protection available under different seasonal conditions. The intimate 

 relation between the vegetation and the lepidopterous fauna of South Africa is thus 

 not merely a question of food ; it is also concerned in many instances ■with various 

 modes of ensuring the survival of a species. 



