THE HOMOLOGIES OF PEDICELLARIE. 401 
separate prongs are toothed and ornamented (Fig. 83, Brissus). 
We frequently find, both in the common spherical Echini and in the 
Fig. 35. Spatangoids, the forks forming 
P either open arches, as in Fig. 84, 
Echinocardium, or very compli- 
cated ball and socket joints, or \ 
independent hemispheres with & 
sharp grooved edges (Fig. 85, 
Pourtalesia). In our flat cake 
urchin ( Echnarachnius) the more 
common pedicellariz have but two forks, with 
sharp teeth along the edges (Fig. 86). 
In the greater num- 
ber of starfishes the 
Fig. 86, 
tively short stems, and 
are as in our common 
starfish (Asteracanth- 
ion) clustered round the 
base of the spines of 
the dorsal surface (Fig. 87) ; though in starfishes we also find tri- 
partite pedicellarie as in sea-urchins, only they are usually sup- 
: rted upon a very short stem, or articulate 
directly from the limestone network of 
Fig. 88, tbe shell. We find 
similarly in Echini 
pedicellariz placed in 
pits (Goniocidaris) in 
za So which the stem is re- 
Niet duced 
Fig. 89. 
ced to a minimum, 
: and their function is 
quite problematical ; their movements are 
reduced to the mere opening and shutting 
of the valves. It is from the study of the 
Pedicellarie of starfishes that we have been able to form some ac- 
Curate idea of the homologies of these interesting appendages. 
We must now go back to the early history of the growth of 
‘pines in embryo Echinoderms to obtain the key of the homolo- 
gies of Pedicellari. In all young echinoderms the test, i.e. the 
AMER, NATURALIST, VOL. VII. 26 
