THE EVIDENCE FROM DEVELOPMENT. 



199 



developed within this larva ; a new mouth and digestive apparatus 

 are produced, and the adult stalked form is assumed. In the Rosy 

 Feather-star such development, with its characteristic modifications, 

 is well seen. Here we first see the oval larva, with its four bands of 

 cilia (Fig. 113, A), and a tuft of these organs at the posterior extremity. 

 Then traces of the future adult (B) appear within this body. As de- 

 velopment proceeds, the cup or body of the Crinoid is formed, the 

 tentacles or arms bud forth, and the young Feather-star, already 

 stalked (c), appears in the likeness of a true Crinoid. Here develop- 

 ment might be thought to have well-nigh attained its limit. So 

 thought the discoverer of this 

 little stalked form, when it was 

 announced that in the Cove of 

 Cork a rara avis in the shape of 

 a British Stalked Crinoid (duly 

 named Pentacrinus Europceus) 

 (Fig. 112, b) had been found. 

 But years afterwards, the little 

 Pentacrinus was seen to leave its 

 stalk, and to appear before the 

 eyes of zoologists in the guise of 

 an old familiar friend the Rosy 

 Feather-star (Fig. 112, a) of the 

 coasts. Thus we discover, firstly, 

 that Crinoids resemble their 

 neighbours the Sea-urchins and 

 Starfishes in the essential details 

 of their development ; and we 

 discover, secondly, in the case of 

 the Rosy Feather- star, a further 

 development of the Crinoid race, 

 in that this latter organism has 

 advanced to a free-living stage. 

 Also noteworthy is the fact, that 

 when existing in its rooted and 

 stalked stage, the Rosy Feather-star closely resembles the ordinary 

 fixed Crinoids, and perhaps bears a still closer likeness to certain 

 fossil members of the group. 



The last class of Echinoderms demanding attention is that of 

 the Holothurians, or Sea-cucumbers (Fig. 108), found around our own 

 coasts, but developed typically as the Trepangs and Beches-de-Mer 

 of tropic seas, and in marketable form as the delicacies of the 

 Chinese. A Sea-cucumber presents us with an elongated body, 

 bearing a tuft of feathery tentacles at the mouth-extremity, and 

 moving by aid of tubular " feet," similar to those of the Starfishes 



FIG. 113. DEVELOPMENT OF CRINOID. 



