ANATOMY OF SHA-URCHINS, 201 
five plates are called the genital plates, while in each of the 
five smaller plates at the end of each ambulacral series is an 
Fig.145.—View of the calcareous net-work 
from a plate of the integument of » Sea-urchin 
(Cidaris). 6, section perpendicular to the hori- 
zontal net-work of straight rods.—After Gegen- 
baur. 
eye-speck. The pedicel- 
larie are three-pronged, 
knob-like spines, scat- 
tered over the body, es- 
pecially near the mouth. 
They partly serve to re- 
move the fecal matter, 
but their main function 
is that of touch. 
Besides the pedicel- 
larie, Lovén has discov- 
ered on most living 
Kchini, with the excep- 
tion of Cidaris, small 
button-like bodies called 
spheridia, situated on a 
short stalk, moving on a 
slightly marked tubercle 
They are supposed to be 
sensorial, probably organs of taste and smell.* 
The internal anatomy of the sea-urchin may be best studied 
$ 
Fig. 146, —Shell of a Sca-urchin (Strongylocentrotius lividus). a, anus; 0e, esophagus; 
#, intestine; s, one of the rods of the tooth-apparatus; m, muscles of the jaws; p, ves- 
sels of the sucking feet; po. extremity of the water-vessel; ca, ocular plate; v, ovary. 
by cutting the shell into two halves, oral and aboral. Remov- 
ing the aboral end, the digestive canal may be seen in place. 
~ In the interambulacral spaces are blue spots, viz., compound eyes. 
