EXPLANATION OF THE PLATES. 



(7) 



stages, which shows the water-tube upon which is 

 developed the actinal area. 



Figs. 3, 5, 11 represent the opposite profiles of the anal 

 extremity of the Brachiolaria, showing the water-tube, 

 upon which is developed the abactinal area. 



Figs. 4, 14 represent the ventral side of the anal extrem- 

 ity of the Brachiolaria, showing the extremities of the 

 actinal and abactinal areas of the Starfish. 



Figs. 6, 7, 8, 9, 13 represent the dorsal side of the anal 

 extremity of the Brachiolaria, in the successive stages 

 of growth of the young Starfish, showing the opposite 

 extremities of the actinal and abactinal areas of the 

 Starfish. 



Owing to the partial transparency of the Brachiolaria, 

 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. 



Fig. 1. Actinal profile of the anal part of the water- 

 tube («>') of the Brachiolaria, previous to the appear- 

 ance of the pentagon of lobes. In stage of PL III. 

 Fig. 7. 



Fig. 2. Somewhat more advanced actinal profile, showing 

 the ambulacral pentagon, as well as the position of 

 the five rods of limestone, opposite the angles of the 

 actinal pentagon, seen through the thickness of the 

 larva on the surface of the other water-tube («>). In 

 stage of PL m. Fig. 8. 



Fig. 3. The 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. 



Fig. 4. The same larva seen from the ventral side of 

 the Brachiolaria, to show the relative position of the 

 pentagons of the two areas ; only two of the rods of 

 the abactinal side are seen, while the edges of three 

 of the actinal folds (t) can be perceived, one above the 

 other, on the foot-like projection formed by the fold- 

 ing of the water-tube iv<. 



Fig. 5. A more advanced Starfish, in stage of PL III. 

 Fig. 10, from the abactinal profile; the Y-shaped ap- 

 pendages of the original rods have increased in number ; 

 smaller independent Y-shaped rods have made their 

 appearance in the intervals between the larger ones, 

 in the spaces corresponding to the middle of the pen- 

 tagon 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. 

 VOL. v. 10 



Fig. 6. The anal part of a larva from the dorsal side, 

 to show the apparent dividing into elliptical compart- 

 ments of the water-tubes (zv, iv 1 ), made by folding and 

 the bending of the extremities of these tubes (PL III. 

 Fig. 10). 



Fig. 7. The same larva from the dorsal side, to show 

 the manner in which the first fold (t) is made on 

 the exterior surface of the wafer-tube 0«'), and the 

 greater size of the right water-tube extending over 

 the digestive cavity to the madreporic opening (b). 



Fig. 8. A Starfish from the dorsal side of the Brachio- 

 laria (PL 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. 



Fig. 9. The same view of a more advanced embryo, 

 somewhat older than PL 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 net-work 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 pro- 

 file ; 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 PL 

 VII. Fig. 8 ; tubercles have formed upon the surface, 

 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. 1 2. The same embryo from the opposite profile ; 

 the inner tentacular folds have become tipped with a 

 triangular point. The thickness of the abactinal sur- 

 face prevents the net-work of cells on the edge of 

 the arms from being seen. 



Fig. 13. A view of the embryo from the dorsal side of 

 the Brachiolaria; the madreporic body (6), the open- 

 ing of the water-pore, is placed at the edge of the 

 upper arm (r"'), the tubercles on the edge of the 

 arms are well shown by the great accumulation of 

 small Y-shaped -rods. 



Fig. 14. The same from the ventral side of the Brachio- 

 laria (PL VII. Fig. 8). This figure shows, perhaps 

 better than any other, the relative position of the 

 extremity of the two pentagonal warped surfaces. 

 The rough outline of the Starfish is due to the man- 

 ner in which the tubercles of the abactinal surface 



