130 



MARINE ANIMALS OF MASSACHUSETTS BAT. 



and it is only then that it can be at once recognized as the yoimg 

 of our common Star-fish. Even then, after it has assumed its ulti- 



Kg. 171. 



Fig. 172. 



mate outline, it lacks some features of the adult, having only two 

 rows of tentacles, whereas the full-grown Star-fish has four. 



Seorwchins. 



This extraordinary process of development which we have ana- 

 lyzed thus at length in the history of the Star-fish, but which is 



Kg. 174. 



lig. 173. 



equally true of all Bchinoderms, has been hitherto described (so 

 far as it was known) under the name of the plutean stages of 



Kg. 171. Lower side of ray of young Star-fish ; m month, b madreporic body, e eye-speck. 



Kg. 172. Toung Star-flsb seen in profile ; t' odd tentacle at extremity of arm. 



Kgs. 173, 174, 175. Young larree of Toxopneustes in different stages of development ; e' - e" arms, 

 v~v" vibratile chord, «ju>' earlets (water-tubes), aodc digestive system, t'~t"' solid rods of arms, 

 m mouth, b madreporic opening. 



