ANJMAJ. PEODUCnON. 265 



the author of this treatise, which is divided into 2 parts, are based on personal 

 observations made on more than 10,500 mice, the experiments dating from 

 November, 1907, to May, 1912. 



Part 1 (pp. 11-^6) is a consideration of the factors producing color in mice. 

 These are classified as formative and distributive color factors. The 3 gen- 

 eral pigment-producing regions in mice were found to be the eye, the skin, and 

 the hair, the pigments produced being limited to yellow, brown, and black. 

 Color is attributed to the formation of melanin pigujent, the product of an 

 oxidation process. It is explained that " the presence of certain distributive 

 factors, or modifications of them, determines what color varieties of mice shall 

 be formed. These distributive factors determine either the total amount of 

 pigmentation or the relative amounts of yellow, brown, and black that are 

 visible." 



Relative to the inheritance of spotting the author states that " experimental 

 evidence does not support a theory which postulates the common origin of 

 white produced by spotting and that produced by albinism." It is further 

 explained that *' present knowledge of spotted forms is too scanty to decide 

 whether spotting is due to a process of loss of the factor for uniformity of pig- 

 mentation, or to a hypostatic restrictive factor. It seems, however, that such 

 spotting as one encounters in guinea pigs, hooded rats, and in many mice, is a 

 unit character subject to enormous quantitative fluctuation, and that it may 

 be considered due to a modification of the factor Y or U which is hypostatic 

 to unmodified or ' self ' forms." 



The observation of Morgan that " in crosses between self and spotted forms, 

 in mice, the spotting seemed modified or contaminated by the cross," was 

 corroborated. In crosses with Japanese waltzing mice, " the spotted individuals 

 of F2 have been contaminated by the cross, having their dorsal pigmentation 

 increased on the average more than 50 per cent over the average of the pure 

 Japanese race." Relative to " whether the various characters are completely 

 independent of each other or whether coupling or gametic association of any 

 sort exists between some of them," it was observed that experiments show no 

 sign of association in the gametes between the several factors or between the 4 

 conditions characteristic of their absence. 



Part 2 of this treatise (pp. 47-102) treats in detail of the experimental data 

 obtained. 



Heredity of tricolor in guinea pigs, H. D. Goodaue and T. H. Morgan (Amer. 

 Nat., 47 {191S), No. 558, pp. 321-3JtS, figs. i45).— Investigations carried on by 

 the authors since 1908 to determine how the different types of tricolor in guinea 

 pigs behave when mated to each other are reported. 



With regard to the question of the heredity of black and white somatic areas, 

 it is concluded that such an area or spot is "a center from which color, if present, 

 is more likely to spread, and, if we assume somatic segregation in an early stage 

 of the embryo the extent of the spot will be a measure of the extent to which 

 a given cell containing the color factor multiplies as compared with neighbor- 

 ing areas that have the white factor. In pigeons the dark w4ng-bar of some 

 breeds may be white in other breeds, although pigment is present elsewhere. 

 We can not assume, of course, a pigment producer to be absent from the germ. 

 It seems more probable that there are special color producers, which if present 

 in the germ, and therefore in all the body cells, give a definite reaction in that 

 region where a white band is formed. In this case there is no localization factor 

 inherent as such, i. e., there is no need to assume somatic segregation, but only 

 germinal segregation of a particular special factor that is realized in a auecial 

 part. The substitution of a white area for a colored one in guinea pigs might 



