164 THE OCEAN 



were taken in a haul of the trawl in 

 555 fathoms, and at another station many 

 hundreds of pycnogonids (Nymphon robustum) 

 were taken in a trawhng from 540 fathoms. 

 This exuberant development of individuals 

 belonging to a single species at one spot in 

 the colder regions of the ocean is believed to 

 be dependent upon direct development, so 

 that the young spread over the sea-bed without 

 the intervention of a pelagic stage. 



In the tow-net catches in the Arctic and 

 Antarctic there are relatively very few pelagic 

 larvae of benthonic species. In the Antarctic 

 the " Challenger " recorded only one echino- 

 derm larva in the surface waters. This was 

 subsequently taken by the British National 

 Antarctic Expedition and by the German 

 South Polar Expedition. It has been de- 

 scribed under the name of Auricularia ant- 

 arctica, and is regarded by Mortensen as 

 the larva of a holothurian. On the other 

 hand, many echinoderms (asterids, ophiurids, 

 echinids and holothurians) were dredged with 

 eggs and with young in various stages of 

 development clinging to the parents. In 

 temperate regions pelagic larvae are abundant 

 during the warmer months of the year, but 

 almost absent in the winter, while in the 

 equatorial regions they are always present in 

 the tow-nets, especially in coastal waters. 



