THE CrENOPHORA. 359 
highest rank among the Actinozoa, and approximates them to the 
sea-anemones. The elegant Plewrobrachia pileus, which in the 
summer so often appears on our coasts in countless multitudes, is 
the species that has beenlongest known. Themelon-shaped body, 
from halfan inch to nearly an inch in length, is clearas crystal, 
and divided by eight longitudinal equidistant ribs into eight 
equally large segments or fields. These ribs are covered with 
numberless flat paddles or cilize, placed one above another, and 
_ obeying the will of the animal. When it wishes to swim back- 
wards or forwards, it sets all its paddles in motion, whose united 
power drives the living crystal rapidly and gracefully through 
the water; and when it wishes to turn, it merely stops their 
movements on one side. In sunlight, the ribs of the pleuro- 
brachia sparkle with all the colours of the rainbow; in dark- 
ness they emit a beantiful cerulean phosphorescence, 
The prehensile apparatus of the elegant little creature is no 
less beautifully organised than its locomotive mechanism. It 
consists of two long tentacles emerging from the under part of 
the body, and capable of so wonderful a contraction as entirely 
to disappear within its cavity, where they are lodged in tubular 
sheaths. On one side they are provided at regular intervals 
with shorter and much thinner filaments, which roll together 
spirally when the chief tentacle contracts, and expand when it 
is stretched forth. On the secondary branches themselves still 
more minute threads are said to have been observed. Words 
are unable to express the beauty which the entire apparatus 
presents in the living animal, or the marvellous ease with which 
it can be alternately contracted, extended, and bent at an 
infinite variety of angles. 
Most of the Ctenophora are spheroidal or ovate, but in 
Cestum elongation takes place to an extraordinary extent, at 
right angles to the direction of the digestive track, a flat ribbon- 
shaped body, three or four feet in length, being the result. The 
Callianire are remarkable for having their ciliated ribs elevated 
on prominent wing-like appendages, and the Beroés, which have 
no tentacles, receive their nourishment through a widely gaping 
mouth, whose size makes them amends for the deficiency ot 
other prehensile organs. Such are but a few of the varieties 
exhibited by the beautiful and interesting Ctenophora. 
In habit they resemble the oceanic Hydrozoa, like them 
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