D.— ZOOLOGY. 89 



zoologist, conscious of the unending diversity of structure and of habits 

 among animals, sees the physiologist's results against a background of 

 which the physiologist himself seems to be sometimes forgetful. 



One hesitates to suppose that the students of heredity are really so 

 forgetful of this background as they sometimes seem to be. No doubt 

 intense specialisation is needed for intense research ; but the Poet of the 

 Brealdast Table, laughing gently at the narrow specialism of the Scarabee, 

 can hardly have foreseen the day when a university in his own country 

 would have upon its teaching staff an officer named in the university 

 calendar as a ' Drosophilist.' 



It is possible, however, that the prevailing lack of interest in questions 

 of phylogeny may have a deeper significance. Those departments of 

 biology that are being most actively studied at the present day are 

 preoccupied with the interplay of forces acting here and now. They 

 ignore the impressions that time may have left on the material of their 

 study. It is as though a crystallographer, studying a pseudomorph, 

 should endeavour to explain its form in terms of its chemical composition 

 and the forces governing the arrangement of its molecules, without taking 

 account of its past history. 



From ignoring anything, it is but a short step to denying its existence, 

 and here, it seems, we have already arrived. Some of you may possibly 

 have listened to a lecture delivered in London in the early part of last year 

 by that very distinguished experimental biologist Dr. Hans Przibram, in 

 which he suggested that we might have to consider the possibility that 

 every species of metazoan had developed independently of all the others 

 from a distinct species of protozoan. The same view was set forth by 

 him in a lecture delivered in Paris on the Theory of Apogenesis (Kev. Gen. 

 Sci. XI, No. 10, 31 May 1929, p. 293). As the English lecture has not been 

 published I will translate as closely as I can from the French one. ' I do 

 not think it likely ' he says, ' that a single substance can have given rise to 

 a general phylogenetic tree according to the classical diagram representing 

 the affinities of species and their distribution in space and time. All the 

 facts would be explained more easily by supposing that there existed, at 

 the beginning, many organised substances developing side by side into 

 species, each of the latter passing through stages more and more advanced 

 without actual relationship of descent between the different species.' 



Many authors have believed in a multiplicity of the primordial forms 

 of life, but few have suggested an independent origin for grades lower than 

 the main phyla. Przibram, with strict logic, has carried the same reasoning 

 down to the individual species. Most biologists with whom I have discussed 

 the matter refuse to take his suggestion seriously. This, I venture to 

 think, is a mistake. Przibram has simply carried to their inevitable 

 conclusion certain lines of thought that we meet with everywhere in current 

 biological literature ; that conclusion is either one of the most significant 

 results of recent biology or it is the reductio ad absurdum of much 

 contemporary work. 



Geneticists have made us familiar with the doctrine of the inalterability 

 of the gene, with its corollary of evolution by loss of factors, which, by the 

 way, seems to differ little from Przibram's Apogenesis. The experi- 

 mentalists have proved (if it wanted proving) the plasticity of the pheno- 



