130 



LECTUEES ON BIOLOGY 



the water-vascular system of the Echinodermata. Above all the 

 mode of formation of these two organs is strikingly similar, for 

 they develop as protusions of the larval intestinal canal (fig. 40). 

 One class of the Echinoderms, the Crinoidea, differs greatly 

 from the rest in the course of its development. Let us choose 

 for illustration a small form which frequently occurs in the 

 Mediterranean, Antedon rosacea. By means of their thin ' arms/ 

 which are furnished with lateral pinnules and processes, they skil- 

 fully climb about in the seaweed. They possess great power of 



FIG. 39. LARVAE OF ECHINODERMATA. 



(1) Common ancestral form ; (2) Pluteus-larva of Sea-urchin ; (3 and 4) Bi- 

 pinnaria- larva of Starfish ; (5 and 6) Auricularia-larva of Sea-cucumber. (After 

 J. Midler.) 



resistance, are easily 'kept ' in an aquarium, and often proceed to 

 reproduction. The enormous tenacity of Antedon is proved by 

 its insensibility to injuries ; one may break off all their ' arms ' 

 without causing them any serious injury; under favourable 

 circumstances they will repair the damage in a short time by 

 regenerating them. 



