620 PROCEEDINGS OF THE AMERICAN ACADEMY. 



7. Albinism apparently complete may in reality conceal traces of the 

 pigment-forming character either in an active or in a latent condition. 

 Albinos thus constituted are in reality mosaics of the contrasted char- 

 acters, but with the pigment-forming character (ordinarily dominant) 

 occurring in a condition of partial or complete latency. When bred to 

 other albinos they uniformly produce albinos, hence they may for con- 

 venience be distinguished as impure recessives. In guinea-pigs and 

 rabbits the impurity of recessive individuals is, in certain cases at least, 

 visible ; in mice it apparently is not. 



8. Cross-breeding is able to bring into activity latent characters or 

 latent elements of a complex character. This is probably the true ex- 

 planation of many cases of reversion. Conversely it is able to cause 

 one or another element of a complex character to become latent and to 

 remain so under close breeding. This principle probably explains how 

 races of black or yellow mice may be obtained by crossing wild gray 

 mice with albinos. 



9. The Mendelian doctrine of gametic purity is fully substantiated 

 by experiments in breeding mice, guinea-pigs, and rabbits, but with the 

 important qualification stated under 8, a qualification which really 

 enhances the practical utility of that doctrine in its every-day application 

 by breeders. 



Bibliography. . 



Bateson, W. 



: 02. Mendel's Principles of Heredity, a Defence. With a Translation 

 of MendeVs Original Papers on Hybridisation, xiv -I- 212 pp. 

 Cambridge. [England. Contains bibliography and portrait of 

 Mendel.] 



Bateson, W., and Saunders, E. R. 



: 02. Experimental Studies on the Physiology of Heredity. Reports 

 to the Evolution Committee of the Royal Society. Report I. 

 160 pp. London. 



Castle, W. E. 



: 03. Note on Mr. Farabee's Observations [on Negro Albinism]. Science, 



N. s., Vol. 17, No. 419, pp. 75-76. 



Castle, W. E. 



: 03^ Mendel's Law of Heredity. Proceed. Amer. Acad. Arts and Sci., 

 Vol ris, No. IS, pp. 535-548. 



