SECTIONAL TRANSACTIONS.— C. D. 359 



is interrupted by erosion and channelling at several well-marked levels, which are 

 frequently characterised by systems of washouts. 



At the base of the Upper Estuarine Series there is evidence of a shallow sea giving 

 place through phases of delta growth and shallow fresh-water lagoons to conditions 

 of delta-swamps, and the preserved fossil floras are seen to change with the altering 

 conditions of deposition. The characteristics of plant-beds which represent floras 

 growing in place on the delta are quite distinct from those of beds made up of drifted 

 fragments. 



SECTION D.— ZOOLOGY. 



(For references to the publication elsewhere of communications entered in the 

 following list of Transactions, see page 445.) 



Thursday, August 5. 



1 . Prof. H. F. OsBORN. — The Problem of the Origin of Species as it appeared 

 to Darwin in 1859 and as it appears to-day. 



In the years 1837 to 1859, when Darwin was writing the ' Origin of Species,' there 

 still prevailed the zoology of Linnaeus and Bufion and the palajontology of Cuvier. 

 The number of mammalian species is estimated at 1,200, as compared with the 12,.500 

 species and sub-species known at the end of the year 1924. Darwin's species stood 

 out like isolated mountain-peaks, whereas to-day living species are often comparable 

 to mountain- chains composed of lesser peaks completely connected by ridges known 

 as intergradations. Similarly, the few extinct species known in Darwin's time are 

 now recognised as terminal stages of often continuous ' descending mutations,' species, 

 genera, and sub-species reaching through hundreds of thousands, if not millions, of 

 years. Thus in both zoology and palaeontology we observe continuity, where Darwin 

 observed discontinuity ; consequently, in 1926 the problem of the ' origin of species ' 

 is absolute! J' different from what it was in 1859. 



Of the vertebrate class, with which we are most familiar, it may be said briefly 

 that the modes of the origin of species are now thoroughly well known, while the 

 causes of the origin of species are far more obscure than in Darwin's day. As to the 

 modes, we may compare aU tliat we may observe in nature as to fishes, amphibians, 

 reptiles, birds and mammals, hving and extinct, and we find that several great 

 principles governing the origin of species emerge from this comparison, chiefly through 

 the testimony of naturalists who have been observing on a world-wide scale, as Darwin 

 himself began to do in the voyage of the Beagle. Similarly, we assemble the observa- 

 tions of palaeontologists working on a world-wide scale, especially in the now wonder- 

 fully complete succession of mammalian life during the Tertiary period. In both 

 zoology and palaeontology these observations include intensive examination of 

 meticulous changes in form, colour, anatomy and habit ; there is also intensive 

 observation of chemical, physical and living environment and of habit, and, in certain 

 cases, of heredity — these being the four coefficients of the origin of species. 



The outstanding conclusion from this comparison is that species originate through 

 a continuous and creative adaptation in either stable or changing conditions of 

 environment. The word ' creation ' must certainly be Unked with the word ' evolu- 

 tion ' to express in human language the age-long origin of species. 



2. Dr. Heslop Harrison. — Induced Mutations and their Significance in 

 Evolution. 



In the industrial areas both on the Continent and in the British Isles melanic 

 forms have arisen in many lepidopterous species. Careful observations made in such 

 districts suggest at once that impurities in the way of metallic salts thrown into the 

 atmosphere as a result of industrial operations are responsible for the phenomena, 

 and, furthermore, that they exert their influence on insects in the larval condition 

 by means of their food-plasts. 



It ought therefore to be possible to induce melanism in susceptible groups. (1) by 

 feedijig non-melanic strains on food-plasts gathered in melanic stations, and (2) by 

 rearing such strains in non-melanic areas on food-plasts artificially charged witb 



