1918J Essciiberg: Distrihution of the Polijnoklae 207 



kind are known in which Polynoidae are found occupying areas that 

 are separated, sometimes by thousands of miles. Considering those 

 species with relatively few individuals and found in widely separated 

 areas, we come to the conclusion that the creatures would never have 

 arrived there by their natural means of locomotion, but that there must 

 be some natural factor or agent facilitating their "distribution. 



One of the best means of dispersal is undoubtedly the oceanic cur- 

 rents. These may influence the distribution indirectly or directly. 

 First, by influencing or changing the temperature of the water. Sec- 

 ondly, by carrjdng terrigenous debris and small oceanic animals to 

 some places, thus preparing better feeding grounds for the Polynoidae. 

 Or the powerful currents may remove the debris from other places 

 leaving the rocks bare and unsheltered, thus changing food conditions. 

 Acting directly the currents may carry adult worms along the bottom 

 of the ocean or in weeds along the surface. The latter mode of trans- 

 portation is known to be true of Nereis. Nereis dumcrilii was collected 

 in the middle Atlantic Ocean (Ramsay, 1913) where it had suposedly 

 drifted from the neighborhood of the Gulf of Mexico with the south- 

 west drift. Nereis niirahilis has been recorded from the coasts of 

 Brazil, Florida, Porto Rico, Bermuda, the Red Sea and the Persian 

 Gulf. Since this species lives and breeds in the algae it is supposed 

 to have been carried out with the floating weeds. 



But the usual way of transportation probably is that of carrying 

 the eggs and pelagic larvae of the worms. If the pelagic larvae hap- 

 pen to be caught in a current, they may drift very rapidly to great 

 distances. This may account wholly for the wide distribution of some 

 of the Polynoidae. 



One would naturally inquire why there are not more annelids 

 scattered in the ocean and why in so many cases only a few specimens 

 of some particular species are found in restricted areas far away from 

 their natural habitat. The reason, apart from imperfections of obser- 

 vations, that only a few individuals of a species are found far away 

 from their original home may be due to their becoming there the prey 

 of natural enemies. The greatest impediment, however, would be the 

 sudden changes of temperature which would destroy the larvae. For 

 instance, the larvae of arctic Polynoidae if carried to tropical zones, 

 would probably be killed by the high temperature of the surface waters. 

 Their survival would depend greatly upon the season in which the 

 larvae were carried, and upon the character of the bottom where they 

 happened to drop in changing from the trochophore to the adult stage. 



