on board H.M.S. 'Challenger.' 535 



all sizes, from the smallest ones to those which have been described with 

 an exogenous growth. Species only occur on the bottom in those places 

 where they are found on the surface. These organisms are found in 

 vast numbers on the surface over regions where there are only a few 

 traces of them or their broken parts on the bottom. 



No living specimen of a Globigerina, an Orbulina, a Pidvinulina, or of 

 the new genera found on the surface, which undoubtedly came from the 

 bottom, has yet been met with. 



The foregoing observations appear to justify the opinion that these 

 organisms live only in the surface and subsurface waters of the ocean. 

 The most potent agent concerned in the removal of these shells from the 

 majority of the deep-sea deposits is very likely that suggested by Pro- 

 fessor Wyville Thomson, viz. carbonic acid; yet there may be others. 

 "Why these shells should be almost entirely absent in some places at a 

 depth of 2000 fathoms, and be abundant in some other few places at a 

 depth of 2900 fathoms, has still to be explained. The tow-net seemed 

 to show that they were as numerous in the surface-waters of the one 

 region as of the other. 



Two varieties of large cells are occasionally noticed in the pelagic 

 Eoraminifera, not unlike the reproductive cells which have been described 

 as occurring in some Infusoria. 



JRadiolaria. — JRadiolaria polyzoa, Acanthometrae, or Polycystinse occur 

 almost universally in the surface-waters of the ocean. As has been 

 stated, they (in a few places in the "Western, Northern, and Middle 

 Pacific) make up a large or principal part of the deposits at the bottom. 

 In very many places they appear to be nearly or quite absent in the 

 bottoms. In some Globigerina- oozes they are present in considerable 

 numbers, in others they cannot be detected. What agents are con- 

 cerned in the removal of these organisms is at this time a matter of 

 conjecture. 



Deep-Sea Rhizopods. — In April 1875 a plan of sending down tow-nets 

 to a great depth was adopted. These were either attached to the dredge 

 and trawl-lines, or sent down separately to a depth of 2000 fathoms or 

 more. This method has been repeatedly practised since, and with these 

 results. 



On every occasion organisms were found in the deep nets which had 

 not hitherto, nor have since, been observed in the nets used near the 

 surface. These appear to have a wide distribution, as the same forms 

 have been taken in the deep nets in the North, Middle, and South Pacific, 

 whilst the surface organisms have varied in these regions to a consider- 

 able extent. These organisms are : — 



Many small crustaceans, usually of a bright orange-colour — Cope- 

 pods, Amphipods, and Cypridinas principally. Many large- sized Eadio- 

 laria, resembling in most respects those forms described by Hackel under 

 the generic name of Galodendrum. 



