404 THE HOMOLOGIES OF PEDICELLARIE. 
(Fig. 100) which eventually become movable and act as pedicel- 
lariæ, though they are the simplest forms of that organ. In an- 
other starfish, the genus Luidia, the central granule surrounded 
by smaller granules develops either into a spine which 
passes through the stages of Fig. 101, and terminates 
in a long slender spine surrounded by papille at its 
base, or the central spine of Fig. 101 is like the central 
granule of Hippasteria, little by little 
split into three, and forms finally a pas- 
sage through such forms as are given in 
Fig. 101 into short tripartite pedicel- 
larize surrounded by isolated spines at 
the base. If anything further were re- 
quired to prove the homology between 
spines and pedicellariæ it is the case of 
Fig, 102. 
Fig. 104. 
upon a tubercle (Fig. 93) surrounded by 
the peculiar smooth area called the scrobicular circle ; 
and this last form.of pedicellariæ is actually found in 
the genus Podocidaris (Fig. 102). The same reasoning 
will readily suggest to the student of Echinoderms the 
homology of the so-called claws of Ophiurans (Fig- 
103) and of the anchors of Holothurians (Fig. 104) which, al- 
though used for such totally different functions, being a sort of 
prehensile organ, for motion along the ground, are in reality only 
in their turn modified spines, or different forms 
of pedicellariz. 
Although the spine (Fig. 94) of our common 
sea-urchin is apparently so different from the 
pedicellariz figured in this article, yet when 
we pass in review the whole order of Echini we 
find differences among the spines fully as great 
as those observed in the pedicellaria. What 
can be more diverse than the immense, slender, 
hollow spine of a Diadema six to eight times the diameter of 
the test, and the short, flattened spine forming a regular pave- 
ment on the test of Colobocentrotus. We find such extremes 
as the club-shaped, curved, ambulacral spines of Salenia, the 
papille of Cidaris, the sharp, solid, curved, antennz-like spines 
Fig. 103, 
(RJ 
one 
