104 THE VOYAGE OF H.M.S. CHALLENGEK. 



When comparing the number of these cavities in the fourth joint of the leg with that 

 of the same organs in a transverse section of the body, — for example, between two lateral 

 processes, where the circumference of the body is in some species nearly the same as that 

 of the fourth joint of the leg, — I observed almost the same number of cavities. This 

 was the case at least in Nymphon hamatxim and in N. hrachyrhynchus ; whereas in 

 the other species more or less considerable diflferences were observed, the number of these 

 cavities in some species being greater in the legs ; in others, on the contrary, round the 

 body. 



With regard to the hairs and spines on the surface of the body, I have already pointed 

 out above that, as a rule, species occurring at great depths are rather smooth, whereas 

 those from shallow water are furnished with numerous hairs and spines. Thus Nymphon 

 longicoxa and N. hamatum have the surface almost quite destitute of spines ; Nymplvon 

 hrevicaudatum and N. hirtipes occurring at moderate depths, the former not exceeding 

 120 fathoms, the latter never reaching 300 fathoms, and generally found in considerably 

 shallower water are the most hairy species of the genus. On the contrary, Nymp>hon 

 hrachyrhynchus, occurring at depths not exceeding 120 fathoms, is almost as smooth 

 as Nym2ohon hamatum. 



The species of Colosse7ideis, and especially the three more accurately studied by me, 

 show almost a perfectly smooth surface. The sensory setse are wanting also in these species ; 

 and the few spines which are present are very short and conical (PI. XVI. fig. 13). Of 

 these three species, two are true deep-sea inhabitants; but the third (Colossendeis 

 prohoscidea, Sab. (sp.), as a rule, is found at a depth not exceeding 200 fathoms. Of the 

 species of Ascorhynchus, the smooth A. glaher is found at a depth of 1375 fathoms ; 

 but the surface of Ascorhynchus orthorhynchus is also not very hairy, yet this species 

 occurs at a depth of only 130 fathoms. 



The shallow water genera Achelia and Ammothea are extremely hairy, whereas in 

 the genus Phoxichilidium some of the deep-sea species (P. pilosum and P. moUissimum) 

 show a particularly hairy surface. Both the spines and the set^ are in these species of 

 a very remarkable length. Finally, Pallene australiensis, occurring at a depth of 38 to 

 120 fathoms, shows again the smooth surface of a true deep-sea species. 



The form of these spines is also very different, but I think it is not necessary to describe 

 them. In some species the spines are not smooth, but serrated ; as, e.g. , in the case of 

 Nymphon hrevicaudatum, Miers, and Pallene australiensis, Hoek (PI. XL figs. 6, 7) ; and as 

 spines having a very curious shape I have pointed out already those of the sixth joint of the 

 ovigerous leg of Nymp)hon longicoxa. No doubt, these must be of great use to the animal in 

 holding the egg-masses, and perhaps also in furnishing a good point for the young ones to 

 cling to. Particularly interesting are also the so-called denticulate spines in the four last 

 joints of the ovigerous legs of most species. I may refer to the descriptive part of this report 

 for an account of their extremely different forms, their numbers, and their arrangement. 



