210 ANATOMY AND PHYSIOLOGY 



Type, Verongia fistulosa, Bowerbank. 



Suborder V. Compound fistulo-fibrous skeletons. 



This suborder is founded on the peculiarities in the 

 structure of the skeleton fibre of a sponge described by me 

 in the ' Annals and Magazine of Natural History' for 

 December, 1845, vol. xvi, p. 405, plate xiii, figs. 1, 2, 

 and also in the account I have given of the fibrous structure 

 of the Spongiadce in this volume. Fig. 268, Plate XIV, 

 represents one of the fibres of the skeleton, X 100 linear, 

 with minute tubular fibres (a) which traverse the central 

 cavity of the large fibres. Fig. 267, Plate XIII, repre- 

 sents a portion of one of the skeleton fibres, exhibiting the 

 secondary canals radiating from the primary ones, X 300 

 linear. 



The genus AuHslda is the only one in which compound 

 fistulo-keratose fibres have been found, and it may be thus 

 characterised : 



AULISKIA, Bowerbank. 



Skeleton kerato-fibrous. Fibres aspiculous, cylindrical, 

 continuously fistulose, primary fistulae having minute 

 csecoid canals radiating from them in every direction. 

 Rete unsymmetrical. 



Suborder VI. Regular, semi-areno-fibrous skeletons. 



The sponges of this suborder have the faculty of appro- 

 priating extraneous matter, such as grains of sand or the 

 spicula of other sponges, which become imbedded in the 

 centre of the cylindrical fibres of their skeletons. The 

 fibres in these cases are regular and cylindrical, and the 

 space between their surfaces and the central line of extra- 

 neous matter is frequently one fourth or one third of their 

 own diameter. The central axis of extraneous matters 



