HIGH SCHOOL ZOOLOGY. 



243 



to the rays, and are provided with 

 reservoirs, from which water can be 

 forced into certain short processes of 

 the steins, known as "tube-feet'' 

 (Fig. 171), which are thus caused to pro- 

 ject from the surface of the body, so as 

 to act as locomotive organs. 



3. The larvae are extremely unlike 

 the adults, the developmental stages 

 recalling in many respects those of a 

 remarkable worm-like animal {Balano- 

 glossus), the organization of which 

 points to its being a very primitive 

 A Hoiothuroid with tentacles fomi, presenting as it does, points of 



expanded, and tube-feet pro- . , t i • 



truded; the latter are arranged COntact With Several higher Sub-king- 

 in distinct rows. , 



doms. 

 4. Of the various classes into which the Echinoderms are 

 subdivided, the Holothuroidea are characterized by cylindrical 

 form and a soft skin (Fig. 171). The tube-feet are often con- 

 fined to a ventral surface so that the animals are then distinctly 



Fig. 171. — Pentacta froiidosa. 

 (U. S. F. C.) 



Fi?. 172. - Sand-Hollar from 

 above. — Echinarach/iins par- 

 iiia. \. Tlie ten double-rows 

 of plates of which the shell is 

 constructed niaj' be seen ; the 

 upper ends of the perforated 

 rows are modified into peta- 

 loid ambulacra. 



Fig. 17?:— Pentaceros from above. 

 A Baharaan Starfish. 



