282 On the Willemoesia Group of Crustacea. 



Alplieus in the young stage is a free-swimming animal 

 with powerful organs of vision; but in its adult condition 

 it burrows in the mud of the sea-bottom, where the eye is 

 of little use, except to see things in close proximity, and 

 where it is liable to injury from rough accidents, unless it 

 were protected, as it is, by the strength of the overlying cara- 

 pace. 



The history of Willemoesia and its allies I believe to be 

 very parallel with that of Alpheus. In its young stage it has 

 well-developed eyes, which it loses when it has arrived at its 

 adult condition. This I believe to be attributable to a similar 

 cause, viz. that it burrows in the soft mud of the deep-sea 

 bottom. 



This is borne out by an examination of the contents of the 

 stomach, which I found to be full of the remains of the 

 structures found in the Olohigerina-oozo,. 



That the depauperized state of the organs of vision is not 

 due to the loss of light from the great depth at which Wille- 

 moesia is taken is evident from the fact that Thalascaris^ n. g. 

 (Crangonidas), is taken at depths equally great, and is remark- 

 able for the large size of its eyes. 



Willemoesia^ moreover, is not one of our deepest sea inhabi- 

 tants. Willemoesia leptodactyla was taken both in the Atlan- 

 tic and Pacific at a depth of 1900 and 1375, while Polycheles 

 Helleri and Pentacheles ohscurus were taken north of New 

 Guinea at a depth of 1070 ; yet most of the other species, even 

 including Polycheles Helleri^ were taken at depths between 

 610 and 120 fathoms. 



The bottom temperature has only been recorded in seven of 

 the stations at which the species were taken — tliat is, only 

 from the deeper soundings ; these, however, vary from 6° 

 to 1°*8 C. I am therefore inclined to think that temperature 

 can only be second to that of the character of the sea- 

 bottom itself. 



Out of the thirteen stations from which specimens of this 

 group have been recorded, the bottom consists of what has 

 been named Qlohigerina-ooz^ in eight, one is recorded of mud, 

 andtwo "r.c." (which, I suppose, means red clay), and one only 

 on hard ground ; but as this occurs only once, and that with 

 an animal {Polycheles Helleri) that is also recorded from 

 another station where Glohigeriyia-ooze exists, I think that we 

 may safely infer that the whole group are inhabitants of a 

 soft bottom, preferring that in which animal life suitable 

 for their existence abounds, and that their general structure 

 and form are in accord with their habitat. 



