42 EMBRYOLOGICAL MONOGRAPHS. 



15. Slightly older than the iireceding figure, b, stomach. 



16. Young embryo, in which tlie deincssion b indicates tlie point where the five tentacles are to force their 



way through. 



17. Embryo, somewhat compressed, to show the calcareous ring, a, round the base of the stone canal, b. 



18. Embryo, seen from the ventral side, compressed, o, mouth ; b, circular ambulacral ring ; c, the five primary 



anibulacral tentacles ; d, the five small calcareous tentacular appendages of the circular canal ; e, the 

 stone canal. 



19. Embryo, seen from the mouth side, a, mouth; /), depression for the five primary ambulacral tentacles of 



the circular canal ; c, depression for the passage of the first pair of ventral ambulacral tentacles. 

 ■20. Emlnyo, seen from the ventral side, compressed, a, mouth ; b, circular vascular ring ; c, ambulacral tentacle. 



21. Embryo, in which tlie oral tentacles have forced their way through ; seen from the dorsal side, with the tenta- 



cles protruded. 



22. Embryo, about iu the stage of fig. 21, seen from the side, compressed, a, mouth ; I, circular canal ; c, oral 



tentacle ; d, stone canal ; e, Polian vesicle ; /, stomach ; g, intestine. 



23. Young embryo, somewhat older tlian the stage of fig. 21, seen in profile. 



2i. Embryo, about in the stage of fig. 23, seen in profile, under compression, a, mouth ; b, digestive sac ; 

 c, anal, and d, oral tentacles ; c, the vesicles of the circular vascular ring at the base of the oral tentacles ; 

 /, calcareous oral ring ; ff, the five longitudinal water-canals ; h, water-tubes leading to the base of the 

 ambulacra ; i, ambulacral tentacles of the ventral side ; k, Polian vesicle ; I, stone canal ; ni, circular oral 

 vascular ring. 



25. Young embryo, seen from the dorsal side, with the first-formed five oral anibulacral tentacles branching, and 



with five new tentacles placed in between them. 



26. Embryo, about in the stage of fig. 25, seen from the mouth side under compression, a, the ten oral ti-ntacles ; 



b, mouth ; c, membranous ring round the actinostome ; (I, outline of the oral calcareous ring ; c, circular 

 water-ring ; /, Polian vesicle ; g, longitudinal water-canal ; k, branch of water-caiial leading to the ventral 

 ambulacral suckers ; i, ventral ambulacral suckers ; !c, transverse muscular bauds ; /, longitudinal muscu- 

 lar bands ; m, stone canal ; n, anus. 



27. Embryo, seen from the dorsal side, with three pairs of ventral ambulacral tentacles, and ten branching oral 



tentacles. 



