130 EXPLANATION- OF THE PLATES. 



PLATE VI. 



The young Starfish after the Brachiolaria has been resorbed. 



Fig. 1. A young Starfish, seen from the actinal side; the anal and oral chisters of arms of the Brachio- 

 laria appear like small knobs, placed on opposite sides of the new mouth. The future rays are mere 

 lobes, and are not symmetrical. 



Fig. 2. The same embryo, seen from the abactinal side, to show the arrangement of the netwoi-k of lime- 

 stone meshes. 



Fig. 3. A more advanced embryo, in which all traces of the appendages of the larva have entirely 

 disajjpeared. Each side of the pentagon of suckers is a rosette made up of seven loops; the limestone 

 particles are deposited so as to project at the angle of the arms between these loops. The mouth is 

 movable, the pentagon is not closed, and the Starfish is not yet symmetrical ; the shape of the different 

 rays is not identical. 



Fig. 4. The same embryo, seen from the abactinal side, showing the arrangement of the successively 

 formed rows of rounded spines and of the plates. The two ends of the open pentagon have approached 

 nearer than in Figs. 1,2; the outline is not yet regular. 



Fig. 5. Magnified view of one of the ambulacra! tubes, with its rudimentary tentacles. 



Fig. 6. The young Starfish, in which the two pentagons have almost closed, and been brought into 

 parallel planes. There has been a great increase in the size of the cut between adjoining rays ; the 

 spines also have grown longer and more pointed ; the limestone points of the angle of the rays 

 have advanced nearer the centre. The Starfish is not quite symmetrical, nor are the arms exactly 

 alike. 



Fig. 7. The same embryo, from the actinal side, shows the great increase of the arabulacral system, the 

 tentacles being distinct pouches on each side of the main tube. The basal tentacles of one system are 

 much further apart than all the others, and this is the last indication that the ambulacral pentagon is 

 not closed. 



Fig. 8. A more magnified view of the actinal side, when the ambulacral pentagon is entirely closed, and 

 the Starfish has become symmetrical, and all the basal suckers are equally distant. 



Fig. 9. The ambulacral system of one arm, when confined by the circle of limestone which has been 

 formed round each ambulacral system ; the first two pairs of tentacles begin to develop disks ; they 

 become club-shaped; the three terminal tentacles are still closely connected, and show no sign of 

 any disk. 



Fig. 10. An abactinal view of one ray and the centre of a young Starfish, in which the spines 

 project far beyond the edge of the disk. The arm-plates and the interradial plates have be- 

 come connected by a narrow bridge. The limestone rods are so much thickened by additional 

 deposits, that they form elliptical cells which have entirely lost the polygonal character of the 

 younger stages. 



Fig. 11. One arm and a portion of the centre, from the abactinal side of the most a<lvanced of the young 

 Starfishes which have been raised by artificial fecundation. The spines are very prominent, long, 

 somewhat spreading, and becoming even fan-shaped. The limestone cells are gradually assuming the 

 character of the limestone cells of the adult, small cells within larger ones ; the cut between the rays 

 is very deep. 



Fig. 12. The same young Starfish as Fig. 11, seen from the actinal side; the three pairs of tentacles 

 have suckers ; the deposit of limestone of the actinal area having the same cellular structure as that of 

 the abactinal area, though formed by the increase of small cells instead of rods. This Starfish also 

 shows the position of the madreporic body, immediately on the edge of the disk of the lower side ; the 

 eye is very prominent at the base of the odd terminal tentacle. The young Starfish (Figs. 11, 12) 

 is about four months old. 



PLATE VII. 



Fig. 1. Two rays and the centre of the Starfish (PL VI. Fig. 10), seen from the actinal side. All 

 the tentacles are encased separately by the limestone deposit of the actinal region. Tlie ten- 

 tacles have grown so long that they extend beyond the edge of the arm. The pair of terminal 

 tentacles has, as yet, increased but little in comparison to the other pairs. The odd terminal 

 tentacle has, at its base, a bright carmine spot, the eye, which appears about this time. The 



