Chap. II. OUTLINE OF THE YOUNG STARFISH. 39 



stories (PL VII. Figs. 3, 4, 5) of circular cells ; the cells of the spine near the edge 

 do not close, but project beyond the margin, giving the spines the appearance of 

 small gothic spires. 



The first row of spines formed — viz.: those immediately on the edge of the rays 

 — increase rapidly, curving sideways, expanding at the tip, and assuming as fantastic 

 shapes as those of Rhabdocidaris • Orbygniana (PL VI. Figs. 10, 11, 12, p p). The 

 other rows of spines, diminishing in size as they approach the centre, are exactly 

 'similar to the former (pi,p 2 ), but not so broad at the extremity, and somewhat more 

 slender. New spines are always added between those originally at the extremity of 

 the rays and the centre of the disk; the latter always remain the most advanced 

 and most prominent of the spines, even when the young Starfish has assumed many 

 more of the features of the adult than it has at present, and has reached a stage 

 when it would not be mistaken for anything but a Starfish, closely allied to our 

 common species. 



Net-worJc of Limestone Cells. — As we have seen in the earliest stages of the Star- 

 fish, there are, on the abactinal area, rods from which, by the addition of Y-shaped 

 processes, clusters of polygonal cells are gradually formed (PL VII. Fig. 7) ; one 

 cluster in the middle of each ray (PL VI. Fig. 10, 4)> one around the smaller rod 

 placed in the angle of the rays (4), and a still smaller one round the rod placed in 

 the very centre of the abactinal area (I). The large clusters extend and unite along 

 the edge of the rays, forming a continuous network ; it is from the cells of the 

 edge that the limestone deposit is formed, which extends over the abactinal surface. 

 The clusters of cells placed in the angle of the rays do not unite laterally, though 

 they become indirectly connected in the more advanced stages of our Starfish, joining 

 with the plates of the rays by a few cells (PL VI. Fig. 10). The central plate 

 remains unconnected with the others in the most advanced of the young which I 

 have raised from the Brachiolaria. The whole of the network is quite movable, 

 and the plates, before they become united, are capable of independent motion by the 

 contraction of different portions of the abactinal area. 



Change of Outline of the young Starfish. — With advancing age, the outline of the 

 young Starfish is greatly modified; at first, when the actinal and abactinal areas are 

 not yet closed, while the larval appendages are still visible on the lower side of the 

 young Starfish (PL VI. Figs. 1, 2), and immediately after the larval appendages have 

 disappeared, and the surfaces of the actinal and abactinal areas are brought t nearer 

 together (PL VI. Figs. 3, 4), it is hardly more than an irregular pentagon, with 

 slightly convex sides, and small rounded notches cut in at the angles (PL VI. Figs. 

 3, 4). These notches become deeper, the arms of the Starfish assume more the 

 appearance of a greek cross (PL VI. Figs. 6, 7) ; the sides of the rays are strongly 

 concave and the concavity is increased with the development of the spines to such 



