234 W. WOODLAND. 
known, lined with the collar cells characteristic of sponges. 
Immediately above the region of these chambers is a short 
space also lined with the choanocytes, but distinguished from 
the rest of the body wall situated below by the absence of 
evaginations, so retaining the primitive asconoid condition. 
Succeeding the choanocytes again is a layer of flat epithelial 
cells which extends to the upper extremity of the sponge, 
where it is reflexed and continued as the exterior dermal coat. 
This internal layer of flat epithelial cells marks out the region 
of the oscular rim, the area which, in these sponges, is alone 
suitable for surface-view observations of the developing 
spicules. The substance of the body wall, bounded internally 
and externally by the gastral and dermal layers respectively, 
is gelatinous in consistency, and contains numerous free cells, 
the majority of which are the scleroblasts concerned in spicule 
formation. 
In mounting the oscular rim for examination it is first 
severed off just below its origin, and the short cylinder thus 
obtained, after having been slit on one side, is laid out flat in 
olycerine (or balsam) on the surface of the slide, preferably 
with its gastral aspect uppermost, and covered. 
Toe SpIcULES IN SYCON CORONATA AND S, CILIATA. 
Three primary forms of spicules occur—the simple monaxon 
and the compound triradiate and quadriradiate. Monaxons 
are present in greatest abundance at the apical extremity of 
the sponge, where they form the “ brush” or circlet of long 
spines, but they also occur in the sponge wall generally, 
through which they protrude, and are especially noticeable at 
the extremities of the chambers where they form projecting 
tufts. In the region of the osculum, i.e. above the region of 
the diverticula, the monaxons all assume a more or less verti- 
cal disposition, but below this region the vertical disposition 
disappears with the development of the diverticula, and the 
arrangement becomes comparatively irregular. 
