ABYSMAL FAUNA. 245 
head. In those animals which have, so to speak, followed an evolu- 
tionary path in the opposite direction, and, instead of evolving 
immense eyes, have suppressed eyes altogether, their place has to 
some extent been taken by a great development of tactile organs. 
Antenne, “barbels,” and tentacles lengthen, and in some cases, e.g. 
some species of Pycnogonid, the legs are enormously elongated, and 
probably act as sensory outposts. 
Another of the peculiarities for which it is difficult to assign an 
adequate reason, is the change that the respiratory organs undergo in 
many abysmal forms. In Crustacea, Mollusca and in Fishes, there 
is often a marked reduction in the size and number of the gill- 
filaments, and in many Tunicata the branchial chamber is profoundly 
modified. In the Isopod Bathynomus, on the other hand, the normal 
respiratory organs of the abdominal appendages have been replaced 
by branching outgrowths of the body-wall full of blood. These are 
protected by the abdominal appendages, which act as opercula. 
All deep-sea animals are carnivorous, and must be so, as no vege- 
tation flourishes in the dark depths of the ocean. Correlated with 
this diet is the large mouth and development of efficient organs for 
capturing prey, and on the other hand, a certain “spiny-ness” which 
is apt to appear in many forms which elsewhere are comparatively 
smooth. The development of these spines may be somewhat of a pro- 
tection against the large mouths just mentioned. Perhaps, more than 
elsewhere on the earth, the depths of the sea bear evidence to the 
truth of the Frenchman’s summing up of Life as the conjugation of 
the verb “I eat,” together with its terrible correlative “I am eaten.” 
It seems probable that most of the bottom dwellers of the Polar 
seas undergo a direct development; at any rate there is a great 
absence of pelagic larvee which might belong to them in the surface 
waters. And in the case of certain Crustacea and Echinoderms from 
the colder waters of both hemispheres such a direct development has 
been observed. 
The Benthos, or abysmal fauna, like the Plankton, or surface and 
swimming fauna, of the Antarctic, contains a number of species and 
genera which are again met with in Arctic circles, but are unknown 
in the intervening oceans. This peculiarity is a factor of the whole 
marine fauna, and not of the deep-sea forms only, and will therefore 
not be further considered here. 
When deep-sea exploration was first undertaken it was thought, 
or at any rate hoped, that the sea would give up many an old-world 
form —living examples of what we know only as fossils—and that 
the abysses of the ocean would yield many a missing link. This has 
