THE HOMOLOGIES OF PEDICELLARIE. 405 
of Coelopleurus, the massive, bat-shaped spines of Heterocentro- 
tus, the cupuli-form spines of Goniocidaris, the slender, silk-like 
spines of the Clypeastroids. Among the Spatangoids, there are 
several families where the spines are specialized along certain 
lines (the so-called fascioles) in which they so retain their embry- 
onic features, being either articulated (Fig. 105) or directly at- 
tached to the test, and provided at the extremity and along the 
Shaft with a more or less sensitive vibratile membrane, as all 
young spines originally are. 
In Ophiurans we find all the intermediate stages between plates, 
claws and slender spines; in starfishes between the simplest 
granules, the most complicated serrated spines and pedicellarix, 
and in Holothurians, between mere spicules, anchors and rig. 105, 
the pavement-like covering of such genera as Cuvieria and AS 
Psolus. All this shows plainly enough that the spines Y 
and pedicellariæ are strictly homologous, whatever modifi- 4 A 
cations they may assume in the different orders of Echino- w 
derms, whether they serve as prehensile scavengers or 
simply protect the test against the violence of the waves 
on the rocks, or the attacks of their enemies. Sea-urchins 
are favorite food of many species of fish who would find it 
rather dangerous to attack the bristling Diademas and re- 
quire pretty strong jaws to get the better of the armored 
Heterocentrotus. The spines are not simply organs of 
defence ; they also act as means of locomotion, and in such 
genera as Arbacia the ambulacral suckers perform only a 
Secondary part in the displacement of the sea-urchin, the 
Spines of the lower side serving as stilts by which the sea-urchin 
raises itself and moves along by a kind of halting gait. In Ophi- 
urans and Holothurians, the pedicellariz hooks and anchors per- 
form the part of organs of prehension and locomotion at the 
Same time. 
There is nothing in the history of the development and in the 
homologies of these organs to show that they have been suddenly 
brought into existence ; on the contrary, the modifications of the 
Spines and pedicellariz as they have been rapidly sketched in this 
article show the most complete homology between appendages 
which have lately been considered as strong proofs of the possi- 
bility of the sudden appearance of organs for which no utilitarian 
motive could be given. I trust I have made it sufficiently plain 
