the headquarters or metropolis of shallow-water starfishes. 

 No other region, so far as known, has anything near so many 

 species, nor so many generic and family types, in shallow 

 water, nor so great an abundance of individuals. The species 

 and genera confined to the deep waters seem equally numer- 

 ous. The abundance and variety of starfishes in these shallow 

 waters is apparently greater than at Panama, the West Indies, 

 or the most favorable parts of the East Indies in similar 

 depths. The coast seems admirably adapted for the perma- 

 nent occupation and evolution of starfishes and similarly for 

 certain other groups of marine invertebrates and fishes." 



The explanation suggested for the great variety, num- 

 bers of individuals and persistence of the starfishes, as well 

 as certain other groups of animals on the Pacific coast of 

 North America is found in the fact that the temperature in 

 this region was not seriously reduced during the Glacial Pe- 

 riod. On the Atlantic coast, on the other hand, these animals 

 were largely exterminated or driven southward. 



Another possible factor is found in the influence of the 

 great Japanese tropical current of water which tempers the 

 climate of the whole coast south of the Aleutian Islands. It 

 is well known that equality of temperature, especially during 

 the breeding season, is a factor of prime importance in the 

 prosperity of most marine animals. 



Number of Rays and Regeneration. Nearly all of the 

 Echinoderms, living or fossil, are normally five-rayed. This 

 pentamerous condition is found in the sea-urchin, sea-cucum- 

 ber, brittle stars as well as in the starfishes. 



This rule of a five-rayed condition has numerous excep- 

 tions among starfishes. Some species normally five-rayed 

 have at times six rays ; such are, Henricia leviuscula, Pisaster 

 ochraceus, Asterias miniata. 



Some species have normally six or more rays while varia- 

 tions show five rays present. Among the multiradiate star- 

 fishes may be mentioned Heliaster with its twenty and in 

 some species as high as forty-four rays. In Pycnopodia the 

 number of adult rays is twenty while the very young stages 

 show six equal rays ; the new rays appear first one on each 

 side of the primary rays, then other pairs just back of these 

 and so on in succession. 



Regeneration of lost parts occurs in starfishes in a marked 

 degree. Specimens are frequently found in which the rays 

 show all degrees of regeneration from the smallest rudiment 

 to a well developed ray. In the case of Linckia columbiae 

 single rays alone are found living and these regenerate the disk 

 with its comet like condition as shown in Plate VI. 



The following list represents most of the starfishes 

 known to occur in Southern California waters. The species 



41 



