THE CTENOPHORA. 359 



highest rank among the Actinozoa, and approximates them to the 

 sea-anemones. The elegant Pleurobrachia pileus, which in the 

 summer so often appears on our coasts in countless multitudes, is 

 the species that has been longest known. The melon-shaped body, 

 from half an inch to nearly an inch in length, is clear as crystal, 

 and divided by eight longitudinal equidistant ribs into eight 

 equally large segments or fields. These ribs are covered with 

 numberless flat paddles or cilise, 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 beautiful 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 fiat ribbon- 

 fihaped body, three or four feet in length, being the result. The 

 Callianirse are remarkable for having their ciliated ribs elevated 

 ■on prominent wing-like appendages, and the Beroes, which have 

 no tentacles, receive their nourishment through a widely gaping 

 mouth, whose size makes them amends for the deficiency of 

 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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