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 racUal 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 sUghtly, 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 \^ery 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 shghtly 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 



