EMBKYOLOGY OF ECHINODERMS. 



127 



At .this stage of the growth of the emhryo, -we have what seems 

 quite a complicated structure, and might be taken for a complete 

 animal ; this is after all but the prelude to its true Star-fish exist- 

 ence. While these various appendages of the embryo have been 

 forming, changes of another kind have taken place ; on one of the 



two water-tubes above mentioned (w')? ^^ t^® ^^^ nearest the di- 

 gestive cavity, a number of lobes are formed (t, Pig. 166) ; this is 

 the first appearance of the tentacles. In the same region of the 

 opposite water-tube (w) a number of little limestone rods arise, 

 which eventually unite to form a continuous network ; this is the 



Hg. us. Adult larva, Bcxalled Brachiolaria, lettering as tiefore ; r back of young Star-fish, ( ten- 

 tules of young Star-fish, ff brachiolar appendages. 



