MATERIALS FOR A MONOGRAPH OF THE ASCONS. 347 
the inclination being greater or less in different parts of the 
spicule, according to the curvature, which is always in a plane 
containing the optic axis; and it is astriking fact that at the 
distal extremity of the spicule the optic axis is at right 
angles to the morphological axis. In other words, 
the oldest part of the monaxon, the part formed when the 
spicule lies entirely in the body-wall, has its optic axis 
orientated in the manner which was, on my view, the primi- 
tive and ancestral one for the spicules of calcareous sponges. 
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