30 HOLASCELLA TARAXACUM. 



Shape and size. The specimen (Plate 21, fig. 8), which is fairly complete 

 apart from the missing upper end, consists of a nearly straight tube, open at 

 both extremities, from the lower, somewhat attenuated end of which arise three 

 dense bundles of root-tuft spicules. The tube is about 120 mm. long and has a 

 circumference of 70 mm. at the upper end and of 40 mm. at the lower. It is 

 now, although rather rigid, considerably compressed and flattened. In the fresh 

 state it probably had a circular transverse section. The wall of the tube, that 

 is the body proper of the sponge, is, for the most part, 2.5-3.5 ram. thick, and 

 perforated by numerous apertures. These apertures are more or less circular 

 in outline, 0.3-1.5 mm. wide, and quite irregularly distributed. Besides these 

 apertures radial canals of similar width, but covered on the outer side by rem- 

 nants of tissue, are observed in the tube-wall. For this reason, on account of 

 their quite irregular distribution, and because the open apertures are destitute 

 of a special marginal membrane, and all the larger and most of the smaller ones 

 are traversed by rays of choanosomal spicules, I do not think that they can be 

 considered as true parietal apertures. I believe myself justified in assuming 

 that the tube-wall is, in the living sponge, continuous and destitute of parietal 

 apertures, and that the openings now observed in it are post mortem artifacts, 

 produced by the shrinkage and partial maceration of the soft parts, and the 

 loss of extensive tracts of the dermal membrane. 



The three root-spicule bundles are very dense, 80-120 mm. long, con- 

 siderably and uniformly curved, and attenuated distally to quite fine points. 

 Proximally they widen out paratangentially and they pass, by the divergence 

 of the spicules composing them, gradually into the lower end of the tubular 

 body. 



Of the three fragments, one is the lower end of a tube similar to the one 

 described above. It is *45 mm. long, circular in transverse section, slightly 

 attenuated below, and open at both ends. Above it has a diameter of 14, below 

 of 12 mm. From its lower end three root-spicule bundles arise. The other two 

 fragments appear to be parts of tubular bodies. 



The colour of the body proper is, in spirit, dirty brown; the root-spicule 

 bundles are colourless. 



Skeleton. The chief support of the body consists of longitudinal and 

 transverse bars, which form a paratangentially extending net with rectangular 

 meshes. This net is composed of the paratangential rays of large stout principal 

 spicules, held together and in position by slender comitals. Most of the prin- 

 cipal spicules are hexactines, a few pentactines and tetractines. Each node of 



