50 CAULOPHACUS SCHULZEI. 
observed only in specimens with discs more than 50 mm. long. Apart from this 
it is also to be noticed that the smaller these apertures are, the better the speci- 
men is preserved. Their great width in indifferently preserved specimens is 
probably due to extreme post mortem shrinkage of the soft parts. 
The canals into which these apertures lead are 0.2-1.5 mm. wide in the best 
preserved specimens (Plate 8, figs. 28, 29). In specimens not so well-preserved 
the largest attain, probably in consequence of excessive shrinkage of the soft 
parts, a width of 3 mm. (Plate 9, figs. 32, 33). 
The spaces between these canals are occupied by a dense, readily stained 
tissue in which are observed traces of oval cavities 120-140 uw long and 70-90 u 
broad, which may be remnants of the walls of the flagellate chambers. 
The stalk is hollow (Plate 9, figs. 27, 33a). I failed to find any open com- 
munication between the cavity of the stalk and the wide canals of the body 
proper. 
The stalk is supported by a tubular network (Plate 9, fig. 27; Plate 10, 
figs. 8, 13, 14) composed of many longitudinal and a few transverse rhabds and 
other megascleres, joined by apposed silica, which solders these spicules together 
where they come in contact, and which forms short rods connecting adjacent 
spicules. It is to be noted also that pinules are embodied in this network (Plate 
10, fig. 8a). The longitudinal rhabds, of which this skeleton-net is chiefly com- 
posed, are in the outer part of the tube situated longitudinally. Towards 
its inner surface their position becomes on the whole more oblique, and here 
transverse rhabds also occur. The (mostly longitudinal) beams of the network 
are usually 20-60, thick, their (mostly transverse) secondary connections 
usually 4-12 u. Above, where the stalk passes into the body of the sponge, the 
longitudinal rhabds of its skeleton become free. ; 
The megascleres of the body are chiefly pinules, hypodermal and hypo- 
gastral pentactines, hexactines, and rhabds. Besides these a few large, not 
hypodermal or hypogastral, pentactine hexactine-derivates have been observed. 
The hexactines and pentactine hexactine-derivates are scattered throughout 
the choanosome. Some of the rhabds are isolated, most of them form bundles, 
which traverse the interior obliquely and extend paratangentially some distance 
below the surface. Hypodermal and hypogastral pentactines, with paratan- 
gential lateral rays and an apical ray directed radially inward, are noticed under 
the dermal and gastral surface. The whole of the surface is occupied by 
pinules, the lateral rays of which extend paratangentially in the superficial 
membrane. The gastral pinules and the dermal pinules of the body and the 
