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these organisms are largely lucifugous, and would tend to collect 
under the shadow of a mass of crinoids as they are known to-do 
under floating logs and driftwood which, thereby, would be placed 
in the economically advantageous attitude of attracting to itself 
without effort its own food supply. The perisome of Uintacrinus 
is black, of such a dense carbonaceous black that it has been 
. preserved without change through the ages which have elapsed since 
cretaceous times; and, if one of these small: lucifugous organisms 
took refuge under the shadow of a mass of Uintacrinus, it would 
be quite likely to be attracted to the blackest portion of the 
animals, the disk or ambulacra, whereupon it would soon find its 
way (or rather be conducted) to the mouth. It is possible that 
the dark colour of many of the large jelly-fish (for instance Cyanea) 
serves to mitigate the glare of the sun-light, and thus to. attract 
under their bells the small animals which serve as food, the absence 
of this advantage being recompensed in the case of such genera 
as Physalia, by an enormous development of the tentacles. 
The embryos of recent crinoids, so far as known, do not float, 
but tend rather in the opposite direction; hence we should infer 
that the embryos of Vintacrinus were also heavier than the surrounding 
medium. Now a floating colony of Uintacrinus during a breeding 
period would be drifted about, as at other times, by the surface 
currents, the waves, and the wind, just as the medusæ are; and, 
consequently, their embryos would fall over a large extent of territory. 
By the time the larvæ from such embryos as happened to fall upon 
suitable bottom had begun to grow, the parent colony would have 
drifted to a very considerable distance, unless, of course, the species 
was an inhabitant of enclosed bays, which, however, taking into 
account its enormous range, is quite unlikely; by the time the 
Young were ready to discard their stems and swim away, forming 
a swarm of their own, the parent colony would be in some remote 
part of the sea. As the position of the parent colony over any 
given area of sea bottom would not be of long duration, the young 
from the embryos which happened to fall at any given place would 
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