10 THE VOYAGE OF H.M.S. CHALLENGER. 
When comparing the bathymetrical range of the different genera with their 
geographical 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 Nymphon, Colossendeis, and 
Phowichilidium. 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 dredged at depths varying 
from 800 to 2800 fathoms. The genus Phowxichilidiwm 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 Pyenogonid 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 Australia, 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. Oorhynchus 
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 material 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, Mr 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). 
