524 
THE YOYAGE OF H.M.S. CHALLENGER. 
there is little doubt that they have been brought up from the bottom of the sea, the 
largest specimens having been taken from the greatest depths. Willemcesia leptodactyla 
(see fig. 181) has -been taken from a depth of 1900 fathoms, or rather more than two 
miles, both in the Pacific and Atlantic Oceans. Polycheles, which is represented by four 
species, has been taken in the Mediterranean and off the coast of Spain, in the Mid 
Atlantic, and off the Fiji Islands, as well as near the Kermadec and New Guinea groups. 
The beautiful Polycheles crucifera (see fig. 182) was captured in the West Indian seas. 
<! The closely- allied genus Pentacheles, which is represented by six species that differ 
from each other in no very remarkable degree in their external features, is scattered over 
a large area, the specimens being captured when the dredge or trawl was let down to 
depths ranging from 120 to 1070 fathoms. They were taken on the western shores of 
South America, around the broken coast, and in the channels between the rocky islands 
that lie along the shore, of Patagonia ; among the Philippine Islands ; from the deeper 
water around New Guinea ; off the Fiji Islands ; 
and from near the New Hebrides. 
“ The organs of vision are entirely absent 
in Eryoneicus (see fig. 183), and are so hidden 
in Willemcesia and the other genera that they 
were long supposed not to exist, and in the 
fossil representative they have not yet been 
detected. 1 It has generally been supposed that 
this rudimentary condition of the organs of 
vision in animals that live in deep waters is 
largely due to their being far beyond the reach 
of sunlight. The genus Glyphocrangon, in 
which the eyes are remarkable for their large 
and well-developed condition, was taken when 
the trawl was sent to great depths, and frequently associated with Willemcesia ; and 
taking the several Stations from which species have been obtained, the average depth of 
the Willemoesian group is less than that of other deep-sea forms in which the eyes are 
large and conspicuous organs. An examination of the embryo before it has quitted the 
egg, shows that in its earliest stages of development the young has organs of vision 
conformable to the ordinary Crustacean type. 
“ The genus Thaumastocheles (fig. 184) taken by the Challenger in the West Indies is 
totally blind, without even the rudiment of an organ of vision. It is related to the 
genus Calocaris of the British seas, which has only very small visual organs, and is also 
allied to Gebia. 
1 In the typical Eryon eyes have never been preserved, but Dr. Woodward figures them as being present in a 
restored figure of Eryon barrovensis, M'CJoy. 
Fig. 183 . — Eryoneicus coccus. After a drawing by von Wille- 
inoes Suhni. a 1 , first antenna: ; eft, second antenna: ; 
p 1 , p 2 , p, p 4 , p^, pereiopoda; st, stomach ; t, testis (?) ; 
i, intestinal canal. 
