208 Universitij of Califoruia PuMications in Zoology [Vol. is 



On the other hand, assuming that the arctic larvae were carried to 

 the lower latitudes in a favorable season, i.e., during the coldest months, 

 the larvae, although they would have more chance to survive on their 

 journey, would nevertheless sooner or later be killed by the temperature 

 if they happened to be driven to warm shallow waters in the tropical 

 zones. Those that were carried to deep waters would find a tempera- 

 ture identical with that of their natural habitat, and would survive 

 and adapt themselves to the new surroundings. Considering their 

 numerous enemies and unfavorable conditions one realizes that there 

 is very little chance for the larvae to survive and probably for that 

 reason we find very few individuals, and those in limited areas far 

 away from their original habitat. Such supposition would explain 

 why the arctic species of Polynoidae, when found on the coasts of Cali- 

 fornia, are so largely deep water inhabitants. As exceptions to this 

 are the cosmopolitan species which are found on these coasts in shallow 

 waters. But it may be that in this species the plasticity and the power 

 of adaptation are more highly developed, so that they would be more 

 fit to survive the vicissitudes of such transportation. Probably for 

 that very reason they are so widely distributed. 



The most powerful oceanic current on this coast aiding in the 

 distribution of the oceanic fauna is the extension of the Kuro Siwo, 

 or Japan Current, flowing along the Pacific coast of North America, 

 striking the American coast at Sitka, Alaska. At this point it broadens 

 out, drifting slowly toward the equator and curving away from the 

 coast. The Japan Current is joined on the west side by the southerly 

 drifting surface waters which increase in volume and breadth until at 

 latitude 25° the current extends more than 1,000 miles ofi" shore 

 (McEwen, 1915). This current undoubtedly serves as a powerful 

 agent of transportation or distribution of species. Probably it is due 

 to the action of this current that species from the coasts of Japan and 

 Alaska have representatives along the coast of California and near 

 the equator. 



lY. The Winds 



In addition to oceanic currents, the winds may be regarded as 

 agents of distribution. The prevailing winds act upon the water, 

 causing cool upwellings of the bottom layers. This has been observed 

 to be the case along most of the Pacific coast of North America. This 

 upwelling water is driven in an easterly direction or toward the shore, 

 thus causing in some parts an inshore cold belt. With the moving body 



