THE HOMOLOGIES OF PEDICELLARIA. 403 
scattered. This is especially the case in such genera as Arbacia 
and the like, in which there are so-called embryonal spines remain- 
ing always fixed im- Fig. 97. 
movably to the test. i 
Fig. 96. 
5 ‘bee : iss In our common star- 
ENA i) Coven fish I have traced the 
© 
earliest stages of th 
spines and pedicellariæ (Fig. 96), and have found that at first it 
is impossible to distinguish between a spine and pedicellariz ; it 
Fig. 98, is only in somewhat later stages that the first 
trace of a difference Fig. 99. 
can be detected (Fig- 
ure 97) ; subsequently $O} oR p. 
there is no doubt what- 
PL 090 
Ze, ever, owing to the 30 33 S| 9 
greater and more rapid Q gu 
development of the central spine, as to ooo 
Fig. 100, what will form spines 6 Ne 
or pedicellariz (Figure 0 Q 
In one of the S009 
pentagonal starfishes of 
our coast (Hippasteria) it is even easier to trace 
the gradual passage of the original limestone network either, on 
the one hand, into a spine, or, on the other, into bipartite pedi- 
cellaric, 
Fig. 101, 
In Fig. 99 we can easily trace the development of a simple 
central granule, surrounded by smaller granules, into a short spine, 
or by the splitting of the granule we have gradually formed a 
slight furrow. , then a deeper groove, till two clappers are formed 
