HOMOLOGIES. 215 
course, united at the base, then stripping it off 
and spreading it out flat, we should have a five- 
rayed star. - But in thus dividing the broad zones 
of the Sea-Urchin into halves, we leave the 
narrow zones in their original relation to them, 
except that every narrow zone, instead of be- 
ing placed between two broad zones, has now 
one half of each. of the zones with which it 
alternated in the Sea-Urchin on either side of 
it, and lies between them. The adjoining wood- 
cut represents a single ray of a Star-Fish, 
One arm of Star-Fish from the oral side. 
drawn from what we call its lower or oral side. 
Along the centre of every such ray, diverging 
from the central opening or the mouth, we have 
a furrow, corresponding exactly to the narrower 
