HOLASCELLA TARAXACUM. 
31 
the net is occupied by the centre of one of these spicules. The two rays of the 
large principal hexactines, which extend longitudinally, are considerably longer 
than the other four. The two rays extending transversely are intermediate in 
size. The two rays extending radially are the shortest, the proximal one, 
pointing towards the axis of the tube, being the shorter of the two. The para- 
tangential rays of most of the principal pentactines and tetractines are simi- 
larly differentiated. The single radial ray of the pentactines points outward. 
Most of the comitals are centrotyle rhabds, a few tri-, pent-, or hexactines. 
Besides these spicules, there have been found in the body of the sponge 
hexactines intermediate in size, very long and slender, longitudinally extend- 
ing rhabds, minute rhabds, micro-tetractines, -pentactines, and -hexactines, 
oxyhexasters, discohexasters, onychhexasters, (calicocomes), and the central 
parts (main-ray crosses) of graphiocomes. The oxyhexasters, onychhexasters, 
graphiocome-centres, and minute rhabds are rare. One or the other of these 
kinds of spicules may possibly be foreign to the sponge. The other spicule- 
forms mentioned are abundant and doubtlessly proper to the sponge. 
Hypodermal and hypogastral hexactines with two axes (four rays) extending 
paratangentially and one axis (two rays) extending radially (vertically to the 
surface) are found below the dermal and the gastral surfaces. The proximal 
ray of these spicules is elongated, the distal ray spined and more or less thick- 
ened. Hexactines of this kind with greatly, and with only slightly, thickened 
distal ray are indiscriminately mingled both in the outer dermal and the inner 
gastral face of the tube-wall. The hypodermal and the hypogastral hexactines 
are very similar. The only difference between them which I could detect is that 
in some of the hypodermals the distal ray attains a greater length than in any 
of the hypogastrals, and that in some of the hypogastrals the lateral rays attain 
a greater length than in any of the hypodermals. It also appears that the 
distal rays of the hypodermals of the lower part of the sponge are on the whole 
thicker than those of the upper part. 
The root-spicule bundles are composed of numerous large, smooth rhabds, 
broken off below, and a few spined monactine anchors. 
The rays of the large principal hexactines (Plate 22, figs. 5, 6, 9, 10, 36; 
Plate 23 , fig. 1 ) are slightly and irregularly curved (Plate 22 , fig. 7) or, more 
rarely, angularly bent (Plate 22, fig. 9), blunt, and usually conic. In very long 
rays (Plate 22, fig. 7) the thickest point is often some distance from the base, 
and such rays are somewhat spindle-shaped. Rarely one of the rays is abnor- 
mally reduced in length and terminally thickened (Plate 22, fig. 6), or divided 
