No. 577] 



NUMBER OF RATS IN ASTERIAS 



35 



amples. Three of these showed a condition which might 

 have arisen either by the fusion of two plates or by the 



division of a single one. The other two cases were simi- 

 lar, but of trefoil form. Dissection showed, in each in- 

 stance, that a single stone canal was present. Therefore 

 these multiple plates had probably arisen by the division 

 of an originally single one. (For a similar condition in 

 A. vulgaris, see Davenport [1901].) Only one multiple 

 madreporite was found in any one individual. 



1. The modal number of rays in Asterias tenuis pina 

 is 7. The range in ray number is from 2 to 9. 



2. The 7-ray condition is uniformly the most frequent, 

 even in widely separated localities. 



3. The modal ray number is the same for animals with 

 subequal rays as for those with a group of regenerating 

 rays. 



4. The evidence indicates that, most commonly, A. 



3 



Summary 



