No. 557] 



NOTES AND LITERATURE 



319 



valuable boreal food fishes everywhere coincides with the iso- 

 therm of 10° C. at a depth of 100 meters. 



Alfred G. Mayer. 



THE GROWTH OF GROUPS IN THE ANIMAL KINGDOM 



Any one who makes an intensive study of many representa- 

 tives of some organism becomes impressed by the fact that they 

 form many slightly differing groups, and is led to ask how these 

 diversities have arisen. This has been the experience of Lloyd 1 

 in studying the rats of India, in connection with the problem of 

 plague prevention. He has therefore been moved to present in 

 book form his impressions as to how the observed groups prob- 

 ably arise, together with the facts on which these impressions are 

 based ; and some general deductions from these impressions. 



The facts observed in the study of the rats are of the following 

 character: (1) Small groups of rats differing in some respects 

 from the forms regarded as typical, occur frequently here and 

 there. (2) Such groups, with the same exceptional characters, 

 appear in various widely separated places, showing that the dif- 

 ferent small groups have arisen independently of each other. 

 (3) "This is true, however, only in the case of groups whose 

 peculiarity appears as a single character unit. Those groups 

 whose peculiarity is made up of several uncorrelated characters 

 arise on one occasion only" (p. 50). Descriptions and figures 

 of many such cases are given : the account here is of much value 

 and interest. 



Such facts naturally lead the author to hold that groups of 

 this sort have arisen by mutation : that is, by a dropping out or 

 alteration of single unit characters, in the Mendelian sense ; that 

 the same character often drops out in different localities, giving 

 rise to small groups of independent origin, yet having the same 

 distinctive features. This part of the discussion would have been 

 given more precision by consideration of the work on inheritance 

 in rodents and other organisms, as carried on by Castle and 

 others. Further, the pure line work with hoinozygotes and in 

 vegetative reproduction might give definiteness to many of the 

 author's rather vague views as to the nature of these groups. 

 The conclusions of Lloyd along these lines will appear somewhat 

 halting and loose to persons steeped in the experimental work in 



'"The Growth of Groups in the Animal Kingdom," by R. E. Lloyd, 

 Longmans, Green and Co., 1912, 185 pp., $1.75. 



