WYVILLE THOMSON 65 



one-fourth of the whole, and describe nearly 1,000 new 

 species, some of which show remarkable modifications 

 induced by life at great depths. Certain of them are totally 

 blind, and others have eyes that are profoundly degenerate 

 in their minute structure and are probably useless as organs 

 of sight. 



Amongst the Pycnogonida, or Sea-Spiders, were some 

 gigantic forms of Colossendeis, measuring about two feet across 

 the outstretched appendages. Although not, of course, a 

 discovery in marine biology, it may be noted here that 

 Moseley was enabled, by the examination of fresh specimens 

 of Peripatus obtained at the Cape, to demonstrate the 

 essentially Tracheate nature of that primitive and annectent 

 form. Living representatives of the fossil Trilobites were 

 eagerly looked for — but never found. 



In the Mollusca, as in Crustacea, we find a tendency for 

 the eyes to degenerate or disappear, in deep water. The 

 " Challenger " collections enabled Pelseneer to establish a 

 phylogenetic classification of the LameUibranchiata based 

 on the structure of the gills, and to show that the pelagic 

 Pteropods are a polyphyletic group, some of which are 

 related to one, and the rest to another, section of the Opistho- 

 branchiata. One of the prizes obtained was the living 

 specimens of Trigonia, dredged off the coast of Australia, a 

 primitive cockle-like form found fossil in European rocks of 

 secondary age, and long supposed to be extinct. 



In the Cephalopoda the single specimen of Spirula, of 

 which only five individuals are known to science, is one of 

 the priceless treasures of the expedition. A living Nautilus 

 pompilius was brought up from 320 fathoms, off Fiji, and 

 Moseley has given us a description of its swimming move- 

 ments in a tub of water on deck. It had been confidently 

 hoped that some deep-sea representatives of those extinct 

 groups, the Ammonites and Belemnites of Mesozoic times, 

 would be found, and Moseley tells us that " even to the last 

 every cuttle-fish which came up in our deep-sea net was 



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