XX. 
CHARACTERISTIC DEEP-SEA TYPES. — ACALEPHS. 
CTENOPHORA AND HYDROMEDUSZ. 
As with fishes, a number of the deep-sea meduse are occa- 
sionally taken at the surface, and undoubtedly many of the rarer 
of our jelly-fishes are deep-water forms which have accidentally 
found their way to the surface. To these probably belongs one 
of the most graceful of our jelly-fishes, 7 "tychogena lactea (Fig. 
422), which swims at a considerable depth below the surface. 
The action of the light, and 
the increase of temperature 
at the surface, suffice to kill 
the animal in a short time. 
As soon as it reaches the 
surface, the disk loses its 
transparency, the genital or- 
gans become dull, and the 
medusa is soon completely 
decomposed, showing that 
the new conditions are to- 
tally unlike those under 
which it habitually thrives. 
From the character of 
di 
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Fig. 422. — Ptychogena lactea. j. 
their development we may 
either find meduse on the 
bottom in their fixed younger hydroid stages, or we may collect 
them alive from the surface in an older stage. Others again are 
always pelagie, swimming freely on the surface in all their stages 
of growth, while a limited number of the so-called deep-sea 
meduse perhaps inhabit the intermediate depths far below the 
