CHAP, v.] GENERAL CONCLUSIONS. 291 



quently slightly discolored by tliein. The forms which oc- 

 curred in such numbers were usually species of the Acantho- 

 metridse ; but Polycystina and the compound genera were also 

 numerous. The remains of Radiolarians were found in all deep- 

 sea deposits, usually in very direct proportion to the numbers 

 occurring on the surface and in intermediate water. It was 

 frequently observed, however, that where, in deep water, certain 

 species swarmed on the surface, very few of their skeletons 

 could be detected on the bottom. This applies especially to 

 the Acanthometridge, and is probably owing to the extreme te- 

 nuity of the siliceous wall of their radiating spicules, which may 

 admit of their being dissolved while sinking to a great depth ; or 

 possibly the spicules may never become thoroughly silicilied, but 

 may retain permanently more or less the condition of acanthin. 

 The Polycystina seem much less destructible, and occur in abun- 

 dance on the bottom at the greatest depths. Although the Ra- 

 diolaria are universally distributed — like the Diatoms, but in a 

 less marked degree — they seem to be most numerous where the 

 specific gravity of the water is low ; they specially swarm in 

 the warm and comparatively still region of the South-western 

 Pacific and among the islands of the Malay Archipelago, where 

 they are much more abundant than in any part of the Atlantic. 

 I have already given the reasons which led us to the belief that 

 Radiolarians inhabit the water of the ocean throughout its en- 

 tire depth, or, at all events, its upj)er and lower portions. 



In the investigations with the towing-net, made by Mr. Mur- 

 ray during the latter part of the cruise — at all depths, the nets, 

 being either sent down independently to the depths required, 

 or attached to the dredge or trawl-rope — about thirty species or 

 more were procured of a beautiful group of minute forms ap- 

 proaching, but in many important points differing from, the 

 Padiolarians. This order have apparently hitherto escaped ob- 

 servation, and I retain for the type genus the name Chal- 

 lengeria, and for the order that of " Challengerida." This 



