AMBULACRAL TENTACLES. 43 



great changes. We will follow these until tlie tentacles have acquired 

 their normal shape, and then return to the changes of the abactinal sur- 

 face. The points of the inner folds of the tentacular pentagon, as seen 

 in PI. V. Figs. 11, 12, t t t, become rounded, forming a rosette, dividing 

 each loop into five lobes. The terminal lol>e in its turn goes through 

 the same process ; two smaller lobes are developed on each side of it 

 (PI. VI. Figs. 3, 5), thus dividing the original simple loop into seven lobes, 

 a terminal one (f), and three pairs {t t t) arranged symmetrically on the 

 sides. The first-formed lobes retain their greater size until the tentacles 

 are well developed, which at first is always in proportion to their prox- 

 imity to the base of the loop. The odd lobe, from which the last pair 

 of tentacles was formed, does not participate in the rapid growth of the 

 others, and is soon outstripped by all the lobes formed along the side of 

 the original loop (PL VI. Figs. 3, 5). The point at which additional 

 tentacles are formed is plainly seen in this early stage of growth ; a pair 

 is always added at the outer extremity of the arm, immediately at the 

 base and on the side of the odd tentacle (the eye-bearing tentacle), which 

 remains at the termination of the ray during the whole life of the Star- 

 fish. It is quite the reverse with the additional spines of the abactinal 

 surface of the disk; they are alwa^^s formed upon the disk, and are 

 pushed out upon the arms by younger spines growing up nearer the 

 centre of the disk. This will be plainly seen when describing more ad- 

 vanced conditions of the young Starfish. As the loops increase, they ex- 

 pand, lose their character of simple folds, and soon become quite extensive 

 sacs {t t t, PI. VI. Fig. 8), opening into the main tube {t"\ from which 

 they were formed, until, finally, they attain the shape represented upon 

 PI. VI. Fig. 9. They soon grow long enough to be quite movable ; they 

 contract at the base, the walls thicken towards their extremity, and they 

 become club-shaped. The result of this contraction is a change of the 

 tentacular cavity into a rudimentary radiating tube (/"), with the ten- 

 tacles attached to it ; it also draws together the first pair of tentacles, 

 which are usually seen in such a way as to appear like knobs (PI. \l. 

 Fig. 5). This basal pair does not lengthen so rapidly as the second pair, 

 which in a couple of days becomes the longest (PI. VI. Fig. 9). Before 

 the base of the radiating tube {t") has contracted, the adjacent basal ten- 

 tacles of adjoining loops are placed nearer together than those of the 

 same basal pair, the basal tentacles thus forming five pairs of tentacles 



7 



