6$$ SCIENCE PROGRESS 



caption of the "growth of groups " is nothing less than the origin of species. We 

 may say at once that, though we do not think that the author has succeeded in 

 his aim, he has certainly collected together some most interesting facts. The 

 discovery that plague was communicated to man by the rat-flea led the Govern- 

 ment of India to take measures to collect and destroy rats on a much larger scale 

 than anything of this kind that had been previously attempted ; it led further to 

 an investigation of the number and distribution of the varieties of rats found in 

 India. It was the privilege of the author to assist in these investigations and 

 from them were derived the ideas which are embodied in this book. 



What Mr. Lloyd has been able to show is briefly this : (i) that Mus rattus, the 

 so-called " old English " black rat, is the dominant species over the greater part 

 of India ; (2) that this species exhibits marked colour varieties and that the most 

 frequent colour variety is not black but greyish brown, very similar in colour, in 

 fact, to the " common " rat of England, Mus norvegicus, from which it, like all 

 varieties of Mus rattus, is separated by a number of anatomical marks ; (3) that 

 these colour-varieties are sometimes confined to definite districts, such as moun- 

 tainous regions but sometimes occur in colonies in the heart of a population 

 consisting of the " normal " variety ; (4) that these colonies may be of any size, 

 from a "group" consisting of two or three individuals to assemblages of much 

 larger size which may include hundreds of individuals. 



He shows further that there is evidence that practically the same variation 

 must have originated independently in widely different centres and that there is 

 some evidences that individuals of the same colour-variety have a tendency to 

 consort and mate together. 



Mr. Lloyd is an ardent believer in the mutation theory of De Vries and, of 

 course, he sees in the distribution of these colour-varieties evidence in support 

 of that theory. According to him there can be no doubt at all that these colour 

 "mutants" have been born (through unknown causes) of " normal " parents and 

 have then proceeded to generate offspring like themselves, which have constituted 

 the group. It is in this way he imagines that new varieties and ultimately new 

 species have come into being. Mr. Lloyd has performed no breeding experi- 

 ments with his mutants and all his evidence consequently is indirect. Now all 

 who know the state of research into problems of heredity at the present day are 

 aware that nothing would give the orthodox Mendelian greater pleasure than to 

 assist at the birth of a new mutation and that the claim of De Vries to have done 

 so is gravely questioned by many of the most trustworthy workers in this field. 

 Mr. Lloyd seems to be totally unaware that the celebrated Oenothera Lamarckia?ia 

 labours under the suspicion of being a hybrid itself and that it is quite possible 

 that the various mutants to which it has given rise may be due to nothing but 

 the segregation of the different factors which have entered into its complicated 

 ancestry. If in the normal population of Mus rattus there exist several strains 

 of heredity which, for all we know, may have existed since Mus rattus was a 

 species at all ; further, if some of these strains are dominant over others, then 

 there will be always a sporadic appearance of apparent new varieties due to special 

 concatenation of circumstances which favour the appearance of recessive strains 

 in certain localities. On the fundamental question of the origin of a new mutation 

 his observations throw no new light. 



We mentioned at the outset that we do not think that Mr. Lloyd had solved 

 the problem of the origin of species. Mr. Lloyd has some caustic comments to 

 make on the different conceptions of species held in practice by different types of 

 naturalist. He is certain that if some of the colour-varieties which he encountered 



