No. 577] NUMBER OF RATS IN ASTERIAS • 29 



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Mod,! Kay 







39 

 36 

 41 



20 

 38 



7 

 7 



2 

 3 



5 



Agar's Isl., 1914 



hTwIuiisIbI., 1914 



Ely's Harbor, 1**14 



Hungry Bay, 1914 



Conev Island. 1914 



The modal number of rays is in each case 7. This is 

 true for the same locality in two successive years, for 

 near-by localities and for places widely enough separated 



to yield critical data relative to the suggestion which 

 prompted this inquiry. For the total population ex- 

 amined the ray frequency distribution, which of course 

 gives a mode of 7 rays, is plotted in Fig. 3. It is to be 

 noted further that according to Ludwig (1897, p. 345) the 

 most common number of rays in A. tenuispina from the 

 Mediterranean is also 7. 



III. It has been observed by every one who has studied 

 A. tenuispina that in most of the individuals the rays oc- 

 cur in two groups, those of one group being longer than 

 those in the other, though within each group the rays are 

 of about the same length. This condition is evident in 

 259 (83.6 per cent.) of my specimens. There is general 



