374 EXPERIMENT STATION RECORD. 



tiou of selection in breeding is to isolate pure strains from a mixed population. 

 It is found in actual experience impossible to bring about by selection improve- 

 ment beyond a point already existing in the pure isolated strain at the beginning. 



The authors suggest that the term " fecundity " be used only to designate the 

 innate potential rei)roductive capacity of the individual organism as denoted by 

 its ability to form and separate from the body mature germ cells, and that the 

 term " fertility " be used to designate the total actual reproductive capacity of 

 pairs of organisms, male and female, as expressed by their ability when mated 

 together to produce individual offspring. "Fertility, according to this view, 

 depends upon and includes fecundity but also a great number of other factors 

 in addition. Clearly it is fertility rather than fecundity which is measured in 

 statistics of births of mammals." 



Our knowledge of melanin color formation and its bearing' on the Men- 

 delian description of heredity, O. Riiidle (BioJ. Bill., 16 {11)09), A'o. 6, pp. 

 SHi-S.jl). — This is a study on the production and inheritance of colors in animals. 



The author thinks that many Mendelian interpretations, and in particular 

 those on color inheritance, are not sound, because some of the factors arise out- 

 side of the germ cell during development as a direct result of tissue differentia- 

 tion quite independent of a definite determiner in the gametes. The basis of 

 the author's objections rests upon the origin and development of melanin pig- 

 ments. The work of the author and other investigators on tyrosin and related 

 aromatic compounds, which are concerned in the production of melanins in the 

 albumen molecule, is briefly reviewed. Melanins are the result of oxidation 

 induced by tyrosinase, a widely distributed oxidizing agent. Each chromogen 

 produces several colors, depending upon the degree of oxidation involved. The 

 melanin colors pass through a series of colors before arriving at the final stage 

 of oxidation, early stages being lighter than later ones. 



Pathogenic conditions in the human body show that the power of an organism 

 to oxidize tyrosin compounds is dependent upon tissue and not upon germinal 

 segregation. Also, the colors of amphibia may be controlled by nutrition. We 

 have thus a long series of color characters which have for a basis the general 

 protoplasmic power to oxidize tyrosin compounds. They are not unit characters 

 but are continuous gradations. The oxidizing power as a process may be 

 strengthened or weakened in the subdivision of nuclear matter during matura- 

 tion, whereas jNIendelian interpretations see only particles segregated. It is 

 stated also that Mendelian interpretors have declared for the doctrine of pre- 

 formation, while the author's theory is essentially epigenetic. It is suggested 

 that further studies may show that other Mendelian discontinuities may have 

 gradations and that other qualitative differences may ajjpear more as quantita- 

 tive sequences. The literature on the subject is appended. 



Facts concerning the determination and inheritance of sex, II. E. Jordan 

 (/■•o/). Bet. Mo., 7','/ (11109), lYo. 6, jip. 5';0-.}o0). — This is a popular review of 

 some recent work on the accessory chromesome and dimorphic spermatozoa and 

 their significance in the determination of sex, which the author summarizes 

 as follows: 



" The present status of the case concerning the determination of sex, as 

 well supported for a large class of plants and animals, appears to be that 

 sex is determined by the spermatozoa (or pollen grains) — which are male and 

 female in the proportion of 1 : 1 — and at the instant of fertilization. But 

 surely it would be the utmost folly to hold on the basis of so comparatively 

 few facts, that this explanation applies universally. Nature arrives at similar 

 ends by devious and divers ways and it is not inconceivable that sex has been 

 attained by several paths, and is now determined in different modes and at 

 different times in the different groups of animals and plants." 



