316 journal of the washington academy op sciences vol. 11, no. 13 



621st meeting 



The 621st meeting of the Biological Society of Washington was held in the 

 lecture hall of the Cosmos Club at 8 p. m., February 19, 1921. Vice-President 

 A. S. Hitchcock presided, and forty seven persons were present. On recom- 

 mendation of the Council, Mr. O. M. Freeman was elected to membership. 



Informal Communications 



Professor E. S. Morse, former president of the Boston Society of Natural 

 History, addressed the Society briefly. The Secretary read by title a paper 

 by S. Stillman Berry: Notes on some Japanese Cephalopods; a review of 

 Sasaki's "Albatross" report. 



Regular Program 



C. E. McClung : Chromosomes in relation to heredity. 



Modem biological work is characterized by greater exactness of methods 

 and by the correlation of effort in different fields. These features are particu- 

 larly marked in studies on heredity in which the existence of separate or unit 

 characters has been determined and their exact numerical distribution 

 observed. Correspondingly, careful and minute studies of the germ cells 

 have revealed a mechanism which supplies a full explanation for the behavior 

 of characters in heredity. Of primary importance is the observation that 

 the character of an organism can be fully known only when the composition 

 of its germ cells is understood. Thus, commonly, when two white animals 

 are bred together, it is expected that their young will be white but cases are 

 known where the result is a progeny of strongly colored coat. Such results 

 are now understood and may be predicted in cases where the nature of the 

 germ cells of the parents is known. The basis of all modern work in genetics 

 was laid by an Austrian monk, Gregor Mendel, in the middle of the last 

 century, but his results emained unknown for fifty years. 



From a study of the mechanism of heredity, as revealed in the germ cells, 

 it is found that the equivalence of the two parents is explained by their equal 

 contribution of a substance, called chromatin, of most highly organized 

 character. As one evidence of this organization the integration into a definite 

 number of bodies, called chromosomes, is observed in every cell in each in- 

 dividual of a given species. Not only is the number exact but the size, form 

 and behavior, so that it is possible to classify some animals by their chromo- 

 somes alone. In the structure and behavior of the chromosomes we find an 

 explanation of the alternative inheritance of contrasting characters, of the 

 chance distribution and recombination of characters, of their transmission in 

 groups, and of breaks in these groups. An exact analysis of the structure 

 of the chromosomes shows them to be made up of definite units whose number, 

 arrangement and movements supply an explanation of the most detailed 

 genetical studies. Finally it has been discovered that a particular chromo- 

 some is concerned with the determination of sex. (Author's abstract.) 



The paper was illustrated by numerous lantern slides, and was discussed 

 by Mr. T. L. Casey. 



Sewall Wright: Heredity as a factor in the resistance of guinea-pigs to 

 tuberculosis. 



The paper described some experiments which have been carried on by 

 cooperation between the Bureau of Animal Industry and Dr. Paul A. Lewis 

 of the Henry Phipps Institute of Philadelphia. The resistance to tuber- 

 culosis has been tested in about 800 guinea-pigs belonging to five closely 

 inbred families, crosses between these families, and in a control stock which has 

 never been inbred. • 



