26 EMBEYOLOGICAL MONOGRAPHS. 



1. Actiiial profile of the anal part of the water -tube (u'') of the Brachiolaria, previous to the appearance of the 



pentagon of lobes. In stage of PI. VII. fig. 27. 



2. Soniewliat more advanced actiual profile, showing the anibulacral pentagon, as well as the position of the ten 



limestone rods r'-r' and r"-r" (the terminal and interradial plates), which are seen through the thickness of 

 the larva on the surface of the other water-tube («■). In a stage iutermediate between those of PI. VII. 

 figs. 30 and 31. 



3. A larva in the same stage as the preceding figure, seen from the opposite profile, to show the abactinal area. 



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 tlie rods of the abactinal side are seen, while the edges of three of the actiual 

 folds (l) can be perceived, one above the other, on the footlike projection formed by the fohliug of the 

 water-tube ic'. 



5. A dorsal view of the Brachiolaria, showing a well-advanced embryo ; the arm-lobes have become indented, the 



arms themselves are separated by a deep cut, the y rods have extended 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 footlike oblique fold of the water-tube. 



6. The same embryo seen from the actinal profile ; the inner tentacular folds have become tipyied with a trian- 



gular point. The thickness of the abactinal surface prevents the network of cells on the edge of the arms 

 from being seen. 



7. The same, from the ventral side of the Brachiolaria. This figure shows, perhaps better than any other, the 



relative position of the extremity of the two yientagonal warped surfaces. The rough outline of the Starfish 

 is due to the manner in which the tubercles of the abactinal surface project aliove it. The Starfish in this 

 condition is at the point of resorbing the larva. The manner in which this resorption takes place is shown 

 on tig. 23 of this Plate. 



8. Quite an advanced embryo Starfish, in which all traces of the appendages of the Brachiolaria have entirely 



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

 ticles are deposited so as to project at the angle of the arms between the tentacular 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. 



9. Magnified view of one of the anibulacral tubes of the ])receding figure, with its rudimentary tentacles. 



10. The young Starfish in which the two pentagons have almost closed, and been brought into jiarallel planes. 



Tliere has been a great im-rease iu the size of the cut between adjoining rays ; the spines also have grown 

 longer and more pointed ; the limestone points of tlie angle of the the rays have advanced nearer the cen- 

 tre. The Starfish is not ipiite symmetrical, nor are all the arras exactly alike. 



11. The same young Starfish, from the actinal side, showing the great increase in size of the anibulacral system. 



The tentacles are now long pouches on each side of the main tube. The basal tentacles of one of the arms 

 are much farther apart than all the othei-s, and this is the last indication that the ambulacral pentagon is 

 not closed. 



12. An abactinal view of one ray, and of the centre of a young Stai-fish, in which the spines project far beyond 



the edge of the disk. The arm-plates and the interradial plates have liccinnc connected by a narrow bridge. 

 The original 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. 



13. One arm and portion of the centre of the most advanced of the young Starfishes which have been raised from 



the Brachiolaria', from the actinal side. The three pairs of tentircles have suckers ; the deposit of limestone 

 of the actinal area has a cellular structure. In this stage the madreporic body is still placed on the lower 

 side, on the very edge of the disk. There is a prominent eye-spot at the base of the odd tciininal tentacle. 

 The young Starfish represented iu figs. 13 and 14 is about four months old. 



1-1. The same young Starfish as fig. 13, seen from the abactinal side ; the spines are very prominent, long, some- 

 what spreading, becoming sometimes even fau-shaped at the extremity. The limestone cells are gradually 

 assuming the character of those of the adult, small cells within larger ones ; the cut between the rays is 

 very deep. 



l.'i. Till' same young Starfish, seen in profile, to show the great development of the abactinal area, and the Echi- 

 nus-like arrangement of the spines in the young St.irfish. The odd tentacle, with the eye at its base, is 

 seen turned up between two of the spines. 



16. Two rays and the centre of a young Starfish, about in the stage of fig. 12, seen from the actinal side, in which 



the ambulacral tube is concealed by the limestone deposit ; the pair of terniiual tentacles has as yet increased 

 but little in sizK in comparison with the other pairs, which have become so long that they extend beyond the 

 edges of the arms. The eye, a brilliant carmine spot, makes its ajipearance at about this stage. The 

 mouth is a well-defined pentagonal opening, limited by the actinal limestone depo.sit. 



17. One of the rays and centre of a young Asteracanthion, about one year old, seen from the abactinal side. 



18. Actinal view of an arm of a young Asteracanthion, probably in its third year. 



19. 20, 21. Magnified views of spines (;)), and of rudimentary pediccllaria; (/>', }•"). 



