Minutes of Proceedings. xvii 



of Tyndall on the great diathermancy of the vapours of ethereal oils, 

 many biologists think that the main function of these oils is to 

 produce a protective atmosphere around the plants, thereby re- 

 ducing their transpiration. If that were the case, one would expect 

 that the excretion of oils should be largest in the driest season and 

 the hottest part of the day. But just the reverse is the case, for 

 many aromatic plants do not betray their presence at such times, 

 while the atmosphere becomes filled with their aroma during foggy 

 weather. Such plants are many Rutaceae, Composites (wormwood), 

 Umbelliferae (Bubon), Palargonium, and even the Ehenosterbush. 

 These facts are, however, in perfect accordance with the view that 

 the oils are a protection against the attacks of herbivorous animals, 

 especially also against snails and slugs, which appear only during 

 wet weather. 



Ordinary Monthly Meeting. 

 Wednesday, June 27, 1906. 

 Dr. J. D. F. Gilchrist in the Chair. 



Miss A. V. Duthie was duly nominated as an Ordinary Member 

 by R. Broom and L. Peringuey. 



Dr. J. D. F. Gilchrist presented a paper on " Opisthobranchiata 

 of South Africa," by Professor Berg, of Copenhagen, containing a 

 description of forty new species, of which several represented new 

 genera. The collection had been made by the Cape Government 

 steamer and in-shore collecting. Both Tectibranchs and Nudibranchs 

 were well represented. Among the former are eight new species of 

 Aptysia. The general difference between the fauna of the East and 

 West Coast was very marked in this group of marine animals, the 

 region west of the Cape Peninsula having forms of northern character, 

 though typically tropical forms of Nudibranchs are not wanting. The 

 region to the east of the Cape of Good Hope has more of a tropical 

 Indian character. 



Dr. R. Broom communicated five papers, four of which were taken 

 as read : — 



(1) " On the Early Development of the Appendicular Skeleton of 

 the Ostrich, with Remarks on the Origin of Birds." It was 

 shown that in the early embryo there are three well-developed 

 toes and two others somewhat rudimentary. In the pelvis 

 the pubis and ischium are directed downwards and united by 



