44 



ZOOLOGY 



Fig. 44. — Bipinnaria with the star- 

 fish budding: from it. e. e', d', g, 

 g'. protuberances of the body 

 comparable with the "arms" of 

 the Brachiolaria figured in the 

 adjoining engraving, b, mouth: 

 o. vent of the larva : A . germ of 

 the star-fish; h. ciliated digestive 

 tract; i, ambulacral rosette (germ 

 of the water- vessels). 



Fig. 45.— Brachiolaria of As- 

 terias vulgaris, enlarged, 

 with the star-fish (r) devel- 

 oping at the aboral end. 

 e, median anal arm; e 6 , odd 

 terminal oral arm;/, brach- 

 iolar arm; /. branch of wa- 

 ter-tube (ww 1 ) leading into 

 /' odd brachiolar arm; /"', 

 surface warts at base of odd 

 brachiolar arm 



Class III. — Echinoidea (Sea-urchins). 



General Characters of Sea-TJrchins. — A good idea of the 

 general structure of sea-urchins may be obtained by an ex- 

 amination of the common sea-urchin, Echinus (Fig. 46), 



Fig. 46 —The common Sea-urchin. Echinus drobachiensis. d, framework of 

 mouth and teeth seen in front; c, the same se^n sideways; a, b, side and ex- 

 ternal view of a single tooth (pyramid); all natural size, 



