558 
ASTRONOMY: F. H. SEARES 
some has yet been obtained that contains both that factor and any 
mutant factor within its ''sphere of influence." 
Backcross tests have shown that males of all the above types with 
respect to Cui and Cur resemble "normal" males in giving no cross- 
overs at all. 
Included in the above tables are a considerable number of data in- 
volving three or more loci at once ; and these agree with the table in show- 
ing clearly that the Hnear order of the factors established for the usual 
second chromosome is unchanged by the factors under discussion. The 
amount of crossing over is altered, often markedly, and not usually 
proportionately in different regions; but the factors keep their same 
sequence. This result serves to emphasize the importance of consider- 
ing the distances on chromosome maps as only diagrammatic, not as 
representing actually proportionate distances between the genes, al- 
though actual distance is evidently an. important factor influencing the 
end result. It does not, I think, in any way weaken the case for the 
chromosome hypothesis, but merely shows, together with the results of 
Bridges^ (1915) and Plough^ (1917), that any chromosome map is avail- 
able for purposes of numerical prediction only when the conditions 
under which it was made are dupHcated. 
1 Some of the early results were reported at the 1913 meeting of the American Naturalists, 
and brief references have been published by me (1915) and by Muller (1916). 
2 Much of this data has not hitherto been published. It has been collected mainly by 
Dr. C. B. Bridges, to whom I am indebted for permission to use it. 
3 Muller, H. J., Amer. Nat., Lancaster, Pa., 50, 1916, (193, 284, 350, 421). 
* Sturtevant, A. H., Zs. Ahst. Vererh., 13, 1915, (234). 
6 Bridges, C. B., /. Exp. ZooL, Wistar Inst. Philadelphia, 19, 1915, (1). 
6 Plough, H. H., these Proceedings, 3, 1917, (553-555). 
FURTHER EVIDENCE ON THE CONCENTRATION OF THE STARS 
TOWARD THE GALAXY 
By Frederick H. Seares 
MOUNT WILSON SOLAR OBSERVATORY. CARNEGIE INSTITUTION OF WASHINGTON 
Communicated by G. E. Hale, July 9. 1917 
In a previous communication' attention was directed to the striking 
difference in the results for the distribution of the stars with respect to 
the galactic plane found by Kapteyn^ and by Chapman and Melotte.^ 
An analysis of the counts of stars on photographs of 88 Selected Areas, 
made at Mount Wilson with the 60-inch reflector, gave preliminary 
values for the variation in the totals to magnitude 17.5 which agree well 
with those of Kapteyn. 
