THE CRINOIDS. 



273 



removed, and the "slugs" boiled for from ten to twenty minutes. After being well soaked in fresh 



water, they are arranged on frames in the curing-house. Here they are smoked and dried by means of 



fires, for which trenches are dug beneath the frames. Four days are required for this curing, after 



which the Trepang must be kept very dry, for it is remarkably hygrometric, and one damp slug will 



spoil a whole bag. The final product is an uninviting, dirty-looking 



substance, which is minced down by the Chinese into a sort of thick 



soup, a favourite dish among many of the European residents in China 



and the Philippine Islands. 



(5) Crinoidea. The Crinoids differ altogether from the other 



Echinoderms in their mode of life. Instead of crawling about mouth 



downwards by the aid of tube-feet, a Crinoid remains more or less 

 permanently fixed in one spot, either lying on its back, or growing on a 

 stalk with its mouth upwards. The Stalked Crinoids or Sea-lilies 

 (Fig. 18) are great rarities at the present day, though they were 

 excessively abundant in the seas of some foi-mer geological periods, 

 their fossil remains being known, as Eiicrinites or Stone-lilies. Their 

 structure, however, is fundamentally similar to that of the Feather- 

 stars (Fig. 19), which we will now proceed to examine. 



As in the. Echinoderms generally, there are five rays, which 

 correspond to the five ambulacra in the test of an Urchin (Fig. 14, A). 

 But each of these five rays may fork from one to seven times, so that 

 the number of arms may fall very little short of two hundred. In 

 those of English seas, however, such as the Rosy Feather-star (Fig. 19), 

 there are rarely more than ten arms. These arms are supported by an 

 internal skeleton of limestone joints placed end to end, and are closely 

 fringed with smaller jointed appendages the pinnules* which spring 

 from them like the barbs from the quill of a feather. This feature 

 sufficiently accounts both for the scientific and for the popular names 

 (Comatula, Feather-star) of these animals. 



Attached to the middle of the back of the Feather-star are a 

 number of little clawed hooks, the cirri (Fig. 20, ci), by which the 

 creature can anchor itself to stones and seaweeds. It detaches itself 

 occasionally, and swims about for a while with a peculiarly graceful 

 alternating movement of its arms, eventually settling down in its pre- 

 vious position, with its arms more or less completely extended. On 

 the upper surface of each arm and pinnule is a groove (Figs. 20, 21, ag), 

 which corresponds to the ambulacral groove on the under side of a Star- 

 fish arm (Fig. 9, ag}. It is lined with cilia, which are in a state of 

 continual vibratory movement, so as to produce currents in the water, 

 that carry tiny food particles towards the mouth, where the grooves of 

 all the arms meet (Fig. 1 9). The mouth may be either almost in the 

 centre of the body or altogether excentric (Fig. 20, M), as in some 

 Urchins. The whole of the coiled digestive tube is lodged within the 

 body (Fig. 20, G), no part of it extending into the arms. It terminates 

 in a tubular projection the anal tube, the position of which depends 

 upon that of the mouth (Fig. 19 ; Fig. 20, at}. 



The body itself consists of two parts: viz., (1) the cup or calyx 

 formed by the skeleton, and (2) the visceral mass or disc, which is 

 supported within this cup. The bottom of the cup is formed by a more or less saucer-shaped 

 piece, the centrodorsal (Fig. 20, cd). Soldered on to this in most Feather-stars are the five first 

 radials (RJ), which correspond to the ocular plates of the Echinoidea. The genital plates of this 

 group are represented by the basal plates of the Crinoid larva (Fig. 8, A, b), which in most Feather-stars 



* Latin, diminutive of pinna,, a feather. 

 273 



Fig. 18. STALKED CKINOID OK 

 SEA-LILY (Pentacrinus wyville- 

 thomsoni). NATURAL SIZE. (After 



Wyville Thomson.) 



