RECENT ADVANCES IN SCIENCE 419 



" The Geographical Races of Galago crassicaudatus," and " On 

 Small Mammals from the Delta of the Parana " (ibid. July 17) 

 11 On the Arrangement of the South-American Rats allied to 

 Oryzomys and Rhipidomys " and " Two New Rats of the Rattus 

 confucianus Group " (ibid. August 17) ; "A New Agouti from 

 the Moon-mountains" (ibid. September 17), all by Thomas: 

 " A New Musk-like Mustela from Java," by Robinson and 

 Thomas (ibid.) : "A New Bat of the Genus Otomops obtained 

 at Durban," by Chubb (Ann. of the Durban Mus. vol. i. July 1 7) ; 

 " Evidence of Multiple Factors in Mice and Rats," by Little 

 (American Nat. July 17). 



General. — " Rats and Evolution " is a subject dealt with by 

 Hagedoorn and Hagedoorn (Amer. Nat. July 191 7). After a 

 full investigation of the various species of rats and their occur- 

 rence, the authors conclude : " All those causes which tend to 

 reduce the potential variability of a group of organisms tend 

 to make varieties or species. Such causes are isolation, migra- 

 tion, adaptation, selection and especially the fact that, either 

 periodically or regularly, the number of individuals of one 

 generation is very much smaller than that of the preceding one. 

 This cause of purification of the type which we see in operation 

 everywhere (think of the numbers of house-flies a year in the 

 first and last generations) operates quite regardless of adapta- 

 tion or fitness. To this cause, working upon variation, may be 

 ascribed numerous characteristics for which we can invent no 

 earthly use, and for which nevertheless species are pure." 



Morgan treats of " The Theory of the Gene " (ibid. Sep- 

 tember 191 7). This paper attempts to define and explain what 

 is meant by a genetic factor and at the same time to meet certain 

 criticisms that have been put forward against various of the 

 hypotheses in genetics. It is pointed out that it is necessary 

 to bear in mind that the mechanism of the distribution of the 

 genes is to be differentiated from the effect produced by the 

 genes through the embryo. The cytoplasm also takes a 

 considerable part and is closely bound up with the environment, 

 which may even alter its constitution. Consequently it leads 

 to confusion to attempt to deduce the mechanism of distribution 

 from the nature of the embryonic reaction. 



Other papers include : " Differentiation by Segregation 

 and Environment in the Developing Organism," by V. Dancha- 

 koff (ibid. July 191 7) ; " Biocharacters as Separable Units 



