ANIMAL PRODUCTION". 361 



melanoblasts, capable of amoeboid motion ; iu others the deposition of pigment 

 has become a hereditary factor, as, e. g., in the choroid coat of the eye or the 

 inlvbag of the squid; in still other cases pigmentation is stimulated into action 

 by internal metabolic processes as well as by external conditions of light, tem- 

 perature and atmospheric gases." 



Hairs and hair pigments, H. Onslow (Etvoicledffe, 37 (1914), No. 550, pp. 

 161-165, figs. 6).— This article deals with the physiological character of hair 

 and hair pigments, in which it is shown that the color of hair depends upon 

 the color and form of the pigment (i. e., whether it is diffused or deposited in 

 granules), and upon the vacuoles. 



Biolog'ical searchlight on race-horse breeding. — VII, The heredity of coat 

 color. VIII, The heredity of gray coat color, J. B. Robertson {Bloodstock 

 Breeders' Rev., 3 (1914), Nos. 1, pp. 16-31; 2, pp. 91-101, fig. i).— After a dis- 

 cussion of the structure of skin and hair and the biochemistry of pigmentation, 

 the author takes up a definition of the various coat colors including chestnut, 

 bay, brown, black, gi-ays and roans, dun, and white or albino, the three basic 

 pigments being black, chocolate, and yellow. 



In considering the behavior of the various colors in heredity it is shown that 

 while the relationship of black to brown and bay, and of brown to bay is not 

 definitely settled, the relationship of these three colors to the three varieties 

 of chestnut is exceedingly simple, for all behave as dominants over chestnut, 

 irrespective of its hue. In practice black, brown, and bay both collectively 

 and severally behave in heredity as alternative characters to chestnut. In 

 proof that chestnuts breed true the author cites the studies made by Bunsow 

 and others, and concludes " no one has been able to bring forward an authentic 

 case of two chestnut thoroughbreds producing aught but chestnut offspring, 

 and there can be not the slightest doubt that chestnuts invariably breed true — 

 and this notwithstanding that their bay, brown, and black ancestors are about 

 four times as numerous as their chestnut ones." 



In demonstrating that pure dominants for black never have chestnut offspring 

 a table is given from which it is noted that " out of the grand total of 11,821 

 matings of these 76 horses, only 16 foals remain permanently recorded as chest- 

 nut, or 0.13 per cent of exceptions. Of these 16, 12 never ran nor were sold 

 at auction, some died young, and the remainder are untraceable." 



The author next draws attention to the fact that the number of those sires 

 which have chestnut grandparents and second, the number of those grand- 

 parents, come out in very close accordance with the law of probability. It is 

 concluded that segregation of alternative factors is a true law in the heredity 

 of coat color, and that the unit characters for black points and absence of 

 black points are transmitted quite independently of all other hereditary units. 



The possible combinations arising in the mating of impure dominant black, 

 brown, and bay sires with impure dominant mares, and also with chestnut 

 mares, are discussed. 



The cause of grayness appears to be a peculiarity in the minute thread-like 

 channels which connect the pigment-producing cells with the hair follicles. It 

 is thought that there is a structural modification in the tiny canals rendering 

 them too small to allow of the passage of pigment granules. This structural 

 peculiarity is transmitted independently of the determining factors for the 

 various coat colors. This view of the cause of grayness, while recently held by 

 Walther, is not accepted by certain other investigators, who regard " grayness " 

 as a unit character which is alternative to black, brown, bay, or chestnut. 



The author points out that in youth the hybrid gray is usually whole colored 

 and gradually develops the inhibitory factor. With exceedingly rare and 



