STAR- FISHES^ 



111 



lowing particulars :— It protrudes from its fore extremity a 

 circle of plumose tentacles, usually branched in all direc- 

 tions like tiny trees. Here is radiism. Down its body 

 run five double rows of suckers, exactly resembling in 

 structure and function those of the Star-fish and Urchin. 

 Here again is radiism. But the arrangement of the in- 

 ternal organs is mostly bilateral. There is a distinct an- 

 terior and posterior extremity. In some species two of 

 the double rows of suckers are undeveloped and useless 

 for progression, and the other three rows are placed on a 

 sort of flat disk, which, therefore, becomes a belly. At 

 length we come to species in which the suckers entirely 

 disappear, the body is lengthened and worm-like, and no 

 trace of the radiate form is left, except the circle of minute 

 tentacles which surround the mouth. Finally these vanish 

 too ; and we find in the obscure Spoonworms (Thalassemia), 

 animals of cylindrical shape, with a proboscis, having a 

 long furrowed appendage on one side, — one of those 

 debateable forms of which naturalists cannot agree in 

 determining the true position ; some assigning it to the 

 Echixodermata, others placing it with the Annelida, 

 or Worms proper. 



A, We have spoken of the suicidal habits of the Brittle- 

 stars. The Sea-cucumbers have the same unhappy ten- 

 dencies, but their modus operandi is different. Sir John 

 Dalyell has observed them lose the tentacles, with the den- 

 tal cylinder, the mouth, oesophagus, lower intestinal parts, 

 and the ovarium, separating from within, and leaving the 

 body an empty sac behind. Yet it does not perish. In 

 three or four months all the lost parts are regenerated, 

 and a new funnel, composed of new branches as long as 



