l8 VERRILL 



species pass through stages corresponding to the adult condition of 

 simpler or more primitive genera, and there is often no way to tell 

 whether a small specimen is mature or not, without comparison with 

 a series. 



HYBRIDISM OF ASSOCIATED SPECIES. 



Owing to the fact that numerous related species of several genera 

 are living together on the Northwest Coast, it is natural to conclude 

 that some of them may frequently hybridize, especially if their 

 breeding seasons are coincident. I have seen many hybrids between 

 Asterias vulgaris and A. forbesi of the New England coast. 



There is considerable evidence that this often occurs on the Pacific 

 Coast, leading to the existence of many very puzzling specimens in 

 some groups. 



I have personally seen a number of apparent hybrids between 

 diverse species of Asterias, Pisaster, Hcnricia, and other genera 

 abundant on that coast. Perhaps some of the equally puzzling speci- 

 mens of Solaster may also be hybrids. 



To determine this matter satisfactorily requires large collections, 

 and especially observations made on the living specimens in their 

 natural environment. The littoral species of Leptasterias that carry 

 their young, abundant on the shores, are eminently adapted for such 

 studies, and are easily raised. 



This can best be done at one of the seaside biological stations, 

 and for that reason I do not propose to discuss the matter at length 

 in this place. Dr. Fisher, also, has found numerous varieties and 

 connecting forms, some of which he thinks may be hybrids, among 

 the large numbers of specimens of Henricia that he has studied. 



It is quite probable that some of the now well established species 

 of starfishes of that coast originated at first as hybrids and that 

 others are now in the process of differentiation into varieties and 

 species. 



FAUNAL RELATIONS AND DISTRIBUTION OF THE SPECIES. 



Details of the distribution of the species must be left to the end of 

 this report, but there are some interesting facts that may well be 

 mentioned here. 



The shallow-water starfish fauna of the Northwest Coast, taken 

 collectively, may be considered as consisting of three parts. 



I St. Those of more southern or tropical origin that have migrated 

 northward to California or beyond. 



