334 SECTIONAL TRANSACTIONS.— D. 



dominant black. In man, the recessive albino is not pure from the dominant pigmented 

 condition, and the recessive blue eye is apparently not pure from the dominant brown. 

 In fox-gloves, the recessive white is not, as a rule, pure from the dominant pigmented 

 condition. In all these cases, the recessive breeds true. How, then, can this trace of 

 the dominant be explained ? It seems inexplicable if the gene is really indivisible. 



But the main importance of the observed impurity of the recessive lies in the fact 

 that it shakes the very foundation on which the postulated indivisibihty of the gene 

 rests. 



Had the recessive been found to be impure in early MendeUan experiments, the 

 hypothesis of the absolute purity of the gamete could never have been put forward 

 and the theory of the indivisibihty of the gene would, therefore, never have been 

 created to account for perfectly clean segregation. 



Dr. R. Broom, F.R.S. — The Origin of the Mammalian Hand. 



A study of the manus and pes in the various groups of the Therapsida shows 

 that the mammalian digital formula arose by the reduction and then loss of one 

 phalanx in digit III and two in digit IV. In Anomodonts, Therocephalians, 

 Dromasaurians and Bauriamorphs the formula is already 2, 3, 3, 3, 3, but in 

 Gorgonopsians it is 2, 3, 4, 5, 3, with reduced phalanges in the third and fourth digits. 

 In Cynodonts {e.g. Thrinaxodon) it is also 2, 3, 4, 5, 3, with the small phalanges still 

 further reduced. 



The curious arrangement of the Epiphyses in the metacarpals is explained by the 

 fact that the first carpal is elongated and functions as a metacarpal. 



Saturday, July 27. 



Excursion to Sea Point and St. James. 



JOHANNESBURG. 



Wednesday, July 31. 



Prof. H. B. Fantham. — Some Remarks on Protozoa found in South African 

 Soils. 



During the last ten years investigations have been made and reports published 

 on the Protozoa found in 335 South African soils examined in water culture and in 

 114 waterlogged soils examined direct (see S. Afr. Journ. Sci., vols, xviii-xxv, 1921- 

 1928). Some Protozoa were found in all the soils examined, the number of species 

 varying from 1 to 30. The total number of species of Protozoa found in all the soils 

 examined was 117. The soils were collected from places in all Provinces of the Union — 

 Basutoland, British Beohuanaland and Mo9ambique ; waterlogged soils were mostly 

 collected near Johannesburg. Cultivated and uncultivated soils, where possible, 

 were examined from each locality. Conditions are very different from those of Great 

 Britain, the soils being partially sterilised by the heat of the sun, and the wet and dry 

 seasons are sharply defined. In the Transvaal, Orange Free State and Natal summer 

 rains prevail, the Western Cape has winter rains, the Cape Midlands are intermediate. 

 Soil cultures were examined daily, usually for three to four months. 



It is very difificult to generalise on individual environmental effects. Darkness 

 had little influence on development rates. Soils containing much humus yielded 

 more kinds of Protozoa than sandy ones, the food supply being greater. Surface 

 soils (0 inches to 6 inches deep) yielded more Protozoa than subsoils. Cultivated 

 soils tended to contain more kinds of Protozoa than uncultivated ones, though 

 exceptions occurred. Daily variations in numbers and the existence of a succession 

 of dominant types of Protozoa have been found. Transvaal and Natal soils collected 

 in the dry season have yielded fewer kinds and smaller numbers of Protozoa than 

 those collected towards the end of the rainy season. Periodic collection and examina- 

 tion of a number of soils have shown the existence of seasonal variation in the composi- 

 tion and quantity of their protozoal fauna, the onset of warmer and moister conditions 

 promoting protozoal activity, while great cold retarded multiplication. 



