THE GENUS COLOBOCENTROTUS. oo 
rence is not limited to the ambulacra near the spheridia, nor are they limited 
tothe ambulacra. They are found both in the ambulacral and interambulacral 
areas and on the actinal as well as the abactinal sides. 
I can only offer suggestions as to the nature of the cystacanths. I have no 
observations of any value regarding their function. They may be modified sac- 
bearing spines such as are found among the Echinothurize or modified pedi- 
cellari# in which the glands have developed into the glands of the cystacanths 
at the expense of the valves. 
