128 EXPLANATION OF THE PLATES. 



Fig. 11. A more advanced larva than Fig. 10, seen from the mouth side, in which the oral arms have 

 assumed all the characters of the anal appendages. The brachiolar arms are quite well developed ; 

 the intestine and the stomach are slightly crowded to one side by the greater increase of the actinal 

 area (t) of the Starfish ; the ambulacral pentagon of the future Starfish is still more marked (I) than 

 in previous stages. Brachiolaria stage. 



Fif. 12. llxe same as Fig. 10 seen in profile, with the mouth downwards. 



PLATE IV. 



Fiw. 1. Seen from the mouth side. A larva with its arms fully developed and in full activity; no fur- 

 ther changes take place in the general aspect of the larva, with the exception of those of the anal 

 part where the Starfish is developing, and those of the brachiolar arms. All the arms are nearly 

 equally advanced, with the exception of the median arms (e), which still retain their greater size. 

 The odd terminal arm (e') has also greatly increased in length, as well as the brachiolar arms (//), 

 which are capable of motion, and into which the branches of the wat«r-tubes can easily be traced. 

 Brachiolaria stage. 



Fig. 2. The same larva, seen from above, on a somewhat smaller scale, shows in what way the stomach 

 and the intestine have been pushed to one side, by the great development of the actinal part of the 

 Starfish, on the right of the figure (s t). The shape of the mouth (m) is particularly well seen, in a 

 dorsal view, at this stage of growth. 



Fig. 3. The same larva on a different scale, seen endways, from the oral end, to show the connection 

 between the pair of brachiolar arms (//) and the oral ventral pair (e'), as well as the position of the 

 odd brachiolar arm (/") at the base of the o<ld terminal arm (e"). 



Fig. 4. An adult larva seen from the right, actinal profile ; the arms are in the position which they take 

 when moving rapidly, arched towards the median arms, the brachiolar arms alone being curved in the 

 opposite direction from the others. Here the crescent-shaped ambulacral pentagon, as well as the 

 lobed pentagonal outline of the abactinal area are plainly seen. 



Fig. 5. A magnified profile view of the brachiolar arms. 



Fig. 6. The brachiolar arms seen from the ventral side of the larva, to show the position of the single 

 disk and of the double row of disks at the base and on each side of the odd brachiolar arm, somewhat 

 less magnified than Fig. 5. 



Fig. 7. The anal j)art of the larva soon after the shrinking of the arms has l»egun. The whole of the 

 terminal anal part of the larva has gradually been absorbed, so that the disk of the Starfish occupies 

 the whole of the space between the median arms, seen from the ventral side ; the oral extremity of 

 the Brachiolaria is unchanged and not represented. 



Fig. 8. The shrinking has gone so far that the whole of the anal part has been affected, and the oral ex- 

 tremity alone, with tlie brachiolar and the terminal arms, retain their original shape and i)roportions. 



Fig. 9. A <lifferent viev/ of the anal part of a larva from that of Fig. 7 ; in a slightly more advanced 

 condition than that of the preceding figure, showing the great height of the abactinal region of the 

 young Starfish ; the oral extremity of the Brachiolaria is omitted, as it remains almost unchanged. 



PLATE V. 



Development of thk Starfish propkr. 



Tlie Figures on this Plate show the gradual development of the actinal and abactinal regions of the Stai^ 

 fish, and the figures rejiresent simply the anal part of the Brachiolariii, which is alone affected during 

 this development. 



Figs. 1-7 correspond to a Brachiolaria, having reached a state about as advanced as that of PI. III. 

 Fig. 10. 



Fig. 8 is a Starfish dcvdopiMl on the Brachiolaria of PI. IV. Fig. 11; while Figs. 9-14 arc stages of 

 development wliich are only found on Brachiolariie having their full complement of arms, and in 

 wliich, exce|)t these changes of the Starfish, but slight modificatijns take place. 



Figs. 1, 2, 10, 12, represent that pmfile of tlie anal part of tlu- Brachiolaria, in successively more advanced 

 stapes, which .»hows the water-tul)e upon wliich is developed the actinal an-a. 



Figs. .1, ."i, II, represent the opposite profiles of the anal extix-mily of tlic Brachiolaria, showing the water- 

 lube, tHK)n which is developed the abactinal area. 



