544 THE AMERICAN NATURALIST [Vol. XLIII 



Hybridism 



One difficulty in these studies arises from the fact that 

 certain of the species, usually very distinct, seem to hy- 

 bridize in localities where their ranges overlap and the 

 breeding seasons are coincident. Owing to the small vari- 

 ations in temperature the breeding season of most species 

 is probably unusually prolonged, and this affords better 

 opportunities for hybridization. Among such apparent 

 hybrids, I will mention particularly those between As- 

 terias epiehlora, a small, usually six-rayed, diplacanthid 

 species, and Pisaster ochraceus (fig. 7), a large, coarse, 

 five-rayed, monacanthid species. The latter ranges from 

 San Diego, Cal., to middle Alaska, and is one of the most 

 abundant littoral species. The former ranges from Puget 

 Sound to the Aleutian Islands. At Sitka and adjacent 

 regions, on rocky shores, it is one of the verv abundant 

 littoral species. Although normally six-rayed', five-rayed 

 specimens are common. It is one of those species that 

 have the habit of carrying the eggs and young attached in 

 clusters around the mouth. 



From Sitka, Wrangel, etc., I have had a considerable 

 number of specimens that appear to be true hvbrids be- 

 tween these two very diverse species. They generally 

 have the small size and form of epiehlora, but some have 

 the reticulated and nodular arrangement of the dorsal 

 spines of ochraceus. And what is still more striking, 

 several of them, looking like true epiehlora, have more or 

 less of the huge, sessile, dentate, dermal pedicellaria? (fig. 

 7) characteristic of ochraceus and the other species of 

 Pisaster. 



I have named six marked varieties of epiehlora, which 

 do not seem to depend on hybridization; or at least I 

 could not satisfy myself of it.* But those that I consider 

 hybrids do not conform to any of the determinate varieties. 

 However, it is easy to understand that if hybrids occur, 

 as I believe they do, between A. epiehlora and A. hexactis, 

 which are much more closely allied and also occur com- 

 monly together, it would not be easy to determine the 



