MUSEUM OF COMPARATIVE ZOOLOGY. 85 
dwell. In the Holothurians as well as in the Actinians we find both the 
contrast and the apparent adaptation to the surroundings. 
This great diversity in coloration brings up interesting questions re- 
garding the influence of the environment upon the fauna at great 
depths. But until we know more of the effects produced by the 
penetration of light through such masses of water, speculations as to 
their cause cannot rest upon a very substantial basis. 
It is difficult to understand how so great and numberiess variations 
may have been brought about, or to account for such a case of mimicry 
as was observed in a crab allied to the Maiadæ, in which the dorsal face 
of the carapace appears like a bit of muddy area covered by corals, with 
a huge white arm resembling a fragment of an Isis-like Gorgonian. 
At present the simplest explanation is that suggested by Moseley, 
that the deep-sea types have little by little found their way into greater 
depths from the littoral limits, and have retained or lost many of the 
features characteristic of their littoral predecessors under conditions 
radically different from those existing in the abysses of the sea. As 
denizens of the littoral belt, they were subject to all the disturbing 
influences of the action of light, of heat, of a varying supply of food, 
and to a certain extent of the motion of the water. All these con- 
ditions are in striking contrast to those we may imagino to exist at 
great depths, where little change can be produced by whatever light 
may find its way to the bottom of an oceanie basin, where the tempera- 
ture is uniform, where there is no motion, and where in fact all the fao- 
tors we are accustomed to associate with marine life as we see it on our 
shores are practically wanting. 
