10 THE VOYAGE OF H.M.S. CHALLENGER. 



When comparing the bathymetrical range of the different genera -n'ith their 

 o-eographical distribution, it is easily remarked that it is the genera most widely 

 spread over the bottom of the sea which are capable of existing at the greatest 

 variety of depth. This is, for instance, the case with Nymjjhon, Colossendeis, and 

 Phoxichilidmm. Some species of Nymphon are found at low-water mark, others 

 inhabiting shallow water in the immediate neighbourhood of the coast are dredged at 

 a depth of under 100 fathoms ; others again are never found at a depth exceeding 800 

 fathoms, and finally, there are some which are true deep-sea species. Some species of 

 Colossendeis were dredged at a depth of under 100 fathoms, other species inhabit the 

 ocean at a depth not exceeding 800 fathoms, and others were cbedged at depths varying 

 from 800 to 2800 fathoms. The genus PhoxichiUdium shows almost the same bathy- 

 metrical range as Nymphon. Now the geographical range of these three genera is, as 

 far as I could ascertain from the facts at my disposal, nearly the same ; this distribution 

 is mundane. With the exception of the Pacific Ocean, from which as yet not a single 

 species of Pycnogonid has been obtained, representatives of these three genera are found 

 almost in every sea. 



Of the genus Ascorhynchus only five species are known as yet. They were collected 

 at depths varying from 38 to 1539 fathoms, and at widely distant places, viz., in the 

 Greenland Sea, between the Cape of Good Hope and Kerguelen Islands, off AustraUa, to 

 the north of New Guinea, and off Japan ; and as the different species of this genus form 

 a very natural group, it is, I think, very probable, that later investigations will show also 

 for interjacent places the occurrence of forms belonging to this same group. Oorhynchtis 

 is as yet the only genus which seems to inhabit depths exceeding 800 fathoms exclusively ; 

 but as only a single specimen of the one species known of this genus has been collected, I 

 do not think it expedient to pay much attention to this fact. 



Hence, with regard to the bathymetrical range, a close study of the mateiial brought 

 home by the Challenger, added to what was previously known on the subject, has 

 shown : — 



(1) That those genera which range most widely geographically are also those which 

 range most widely in depth ; and (2), that there does not seem to exist a single true 

 deep-sea genus of Pycnogonids.^ 



As for the influence of the increasing depth on the form and the structure of our 

 animals, this is by no means easily traced. As far as the structure of the integu- 

 ment and of the eyes is concerned, I will treat the question at some length when speak- 

 ing of their structure. As a rule the true deep-sea species are more slender, the legs very 

 long and brittle, and the surface of the body smooth, whereas the true shore-inhabitants 

 are much more concentrated, have shorter legs, and are often densely covered with 



1 From the study of deep-sea forms in general, Jlr Moseley and others came to the conclusion that these animals 

 have a world-wide range. Of this the Pycnogonids give a fair instance, I believe (Moseley in Nature, April 8, 1880 

 p. 546). 



