EXPLANATION OF THE PLATES. 129 



Fics. 4, 14, represent the ventral side of the anal extremity of the Braehiolaria, showing the extremities of 

 the actinal and abactinal areas of the Starfish. 



Fin-s. 6-9, 13, represent the dorsal side of the anal extremity of the Bratliiolaria, in the successive 

 stao-es of wrowth of the young Starfish, showing the opposite extremities of the actinal and abactinal 

 areas of the Starfish. 



Owinc to the partial transparency of the Braehiolaria, either the actinal or the abactinal area is always 

 projected upon the other, when the larva is seen in profile. In the dorsal or ventral views, the angle 

 made by the actinal and abactinal areas becomes visible. 



Fi"-. 1. Actinal profile of the anal part of the water-tube («>') of the Bracliiolaria, previous to the appear- 

 ance of the pentagon of lobes. In stage of PI. III. Fig. 7. 



Fie. 2. Somewhat more advanced actinal profile, showing the ambulacral pentagon, as well as the posi- 

 tion of the five rods of limestone, opposite the angles of the actinal pentagon, seen through the thick- 

 ness of the larva on the surface of the other water-tube (w). In Stage of PI. III. Fig. 8. 



Fif. 3. Tlie same larva seen from the opposite profile, to show the abactinal area ; small Y-shaped rods 

 have appeared at the extremities of the simple rods. 



Fin-. 4. The same larva seen from the ventral side of the Braehiolaria, to show the relative position of 

 the pentagons of the two areas; only two of the rods of the abactinal side are seen, wliile the edges 

 of three of the actinal folds Q) can be perceived, one above the other, on the foot-like projection 

 formed by the folding of the water-tube w'. 



Fl"-. 5. A more advanced Starfish, in stage of PI. III. Fig. 10, from the abactinal profile ; the Y-shaped 

 appendages of the original rods have increased in number ; smaller independent Y-shaped rods have 

 made their appearance in tlie intervals between the larger ones, in the spaces corresponding to the 

 middle of the pentagon of the actinal side. The angles of the actinal pentagon are formed of a double 

 fold, the sides of which are concave ; the stomach is almost concealed by the great accumulation of 

 limestone granules on the abactinal area. 



Fif. 6. Tlie anal part of a larva from the dorsal- side, to sliow the apparent dividing into elliptical com- 

 partments of the water-tubes (ic, to'), made by folding and the bending of the extremities of these 

 tubes (PI. III. Fig. 10). 



Fi<T. 7. The same larva from the dorsal side, to show the manner in which the first fold (I) is made on 

 the exterior surface of the water-tube (w'), and the greater size of the right water-tube extending 

 over the digestive cavity to the madreporic opening (i). 



Fig. 8. A Starfish from the dorsal side of the Braehiolaria (PI. III. Fig. 11) ; shows the lobes formed by 

 the two arms which are in view, with the large cluster of rods in the centre of the lobe, and the 

 small cluster in the space opposite the angle of two lobes. 



Ficf. 9. The same view of a more advanced embryo, somewhat older than PI. IV. Figs. 1, 2; the lobes of 

 the arms have become indented, the arms themselves are separated by a deep cut, the Y-rods extend 

 so as to form almost a continuous network over the whole abactinal area. The actinal pentagon has 

 assumed the shape of prominent loops projecting beyond the foot-like, oblique fold of the water-tube. 



Fig. 10. The same embryo, seen from the actinal profile; the tentacular loops stand out independently 

 from the surface of the water-tube ; the stomach and nearly the whole length of the intestine are 

 enclosed by the abactinal area. 



Fig. 11. Seen from the abactinal profile in stage of PI. VII. Fig. 8; tubercles have formed upon the sur- 

 face, the Y-shaped rods extend into them, the lobes of the edge of the disk are deeper, the second 

 set of clusters of limestone cells have greatly increased. 



Fig. 12. The same embryo from the opposite profile; the inner tentacular folds have become tipped with 

 a triangular point. The thickness of the abactinal surface prevents the network of cells on the edge of 

 the arms from being seen. 



Fig. 13. A view of the embryo from the dorsal side of the Braehiolaria; the madreporic body (6), the 

 opening of the water-pore, is placed at the edge of the upper arm (?","'), the tubercles on the edge of 

 the arms are well shown by the great accumulation of small Y-sh:iped rods. 



Fig. 14. The same from the ventral side of the Braehiolaria (PI. VII. Fig. 8). This figure shows, per- 

 haps better than any other, the relative position of the extremity of the two pentagonal warped sur- 

 faces. The rough outline of the Starfish is due to the manner in which the tubercles of the abactinal 

 surface project above. The Starfish in this condition is at the point of resorbing the larva, and of 

 closing the actinal and abactinal areas. 



