ANIMAL PRODUCTION. 473 



The thymus and sexual organs. — III, Their relationship to the growth of 

 the animal, D. N. Paton {Jour. Physiol., 42 (1911), No. Jt, pp. 261-282, fig. 1).— 

 The removal of the thymus retarded, the growth of the testes in young guinea 

 pigs, but not in those weighing above 300 gm. The simultaneous removal of 

 the thymus and testes in very young guinea pigs checked the growth of the 

 animals, but the removal of the testes or thymus alone had no effect upon 

 the growth. Female guinea pigs deprived of the thymus at an early age became 

 pregnant about the same time as normal animals. Ovariotomy and ovariotomy 

 with thynjus extraction appeared to exercise no effect on the rate of growth of 

 the immature females. 



These results indicate that in the guinea pig both the thymus and testes 

 exercise an influence on the growth of immature animals, and that after the 

 removal of one of these organs the other can compensate in part at least for 

 the loss of the other. 



On metallic coloring in birds and insects, A. A. Michelson {Phil. Mag. and 

 Jour. 8ci., 21 {1911), No. 12^, pp. 55^-567 ) .—This is a study of the iridescent 

 plumage of pigeons, peacocks, fowls, butterflies, and other animals caused by 

 reflected light as distinguished from the colors due directly to pigments. In 

 optical tests with polarized light measurements were made of the phase dif- 

 ferences and amplitude ratios for various angles of incidence. The difficulty en- 

 countered by the absence of a true optical surface was met by replacing the 

 objective collimator and of the observing telescope by low-power microscope 

 objectives of small aperture. 



The results indicate that the iridescence is due to an extremely thin film of 

 some substances closely analogous in optical qualities to thin films of anilin 

 dyes. 



Experimental investigations on the inheritance of hyperdactylism of 

 fowls. — III, Control experiments and experiments with common fowls, D. 

 Barfukth {Arch. Eniwichi. Mech. Organ., 31 {1911), No. 3. pp. -',79-51J).-— 

 Hyperdactylism in common fowls was found to be inherited independently of 

 sex, as in the case of Orpingtons (E. S. R., 21, p. 572), and may remain latent 

 over one generation. The author does not think hyperdactylism is inherited in 

 Mendelian proportion. 



Inheritance of fecundity in the domestic fowl, R. Pearl {Amer. Nat., JfS 

 {1911), No. 53). pp. 321-3.'io. figs. 5). — The purpose of this paper was to present 

 figures sufficient to indicate with some degree of probability that egg production 

 in fowls is inherited, and " probably inherited in accord with the genotyiie con- 

 cept in spite of the fact that we do not and can not here have pure lines in 

 the strict sense of Johannsen's definition." 



The winter egg production of each generation of represented pedigrees show- 

 ing high and low fecundity lines are presented in graphic form. The aim since 

 1907 has been to discover and propagate genotypes of high and low fecundity, 

 and the effectiveness of the selection is shown in the following mean winter 

 production with high fecundity lines: 1908-9, 54.16; 1909-10, 47.57; 1910-11, 

 50.58, as compared with 22.06, 25.05, and 17, respectively, for all low fecundity 

 lines. Effectiveness of selection within the genotype was found to be without 

 influence. 



The differentiation of sex and the relation of the sex in chicks, E. Thom- 

 SEN {Arch. EnHcicM. Mech. Organ.. 31 {1911), No. 3, pp. 512-530, p/s. 2).— The 

 sex of incubating chicks could be determined microscopically on the fifth day, 

 and maci'oscopically on the ninth day. The secondary sexual characters were 

 established before hatching. Of 805 chicks 385 were males. 



A bibliography is appended. 



