AOT) PHYSIOLOGY OF THE SPONGIADiE. 
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in his ‘Tabular View of the Animal Kingdom,’ published in 1861, to represent that por- 
tion of them which agree in structure with the well-known species described in the 
‘ History of the British Sponges ’ as Halichondria oculata. Part II. Plate XXVII. fig. 8. 
Suborder IV. Simple fistulo-kerato-fibrous skeletons. 
The type of this suborder is Lamarck’s Spongia fistulosa. The anatomical structure 
and the general habits of the sponges of this description are so widely different from the 
true Spongias, that I was induced to establish them as a separate genus, and I accord- 
ingly designated and described them as such in the Annals and Magazine of Natural 
History for December 1845, vol. xvi. p. 400, plate 13. fig. 7. It is unnecessary to enter 
here into a detailed account of these tissues, as I have described the peculiarities of the 
structure of the simple fistulo-keratose fibrous skeletons at length in the second part of 
this paper at p. 755, and figured the tissue in Plate XXVII. fig. 12. 
The genus may be characterized as follows : — 
Verongia, Bowerbank. 
Spongia, Lamarck. 
Skeleton kerato-fibrous. Fibres cylindrical, continuously fistulose, aspiculous. Rete 
unsymmetrical. 
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. x\i. p. 405, plate 13. figs. 1 & 2, and also in the second part of this paper, 
p. 756, and figured in Plate XXVII. figs. 13 & 14. 
The genus AulisMa is the only one in which compound fistulo-keratose fibres have 
been found, and it may be thus characterized : — 
Auliskia, Bowerbank. 
Skeleton kerato-fibrous. Fibres aspiculous, cylindrical, continuously fistulose ; primary 
fistulre having minute caecoid 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 appropriating 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 extraneous 
matter is frequently one-fourth or one-third of their own diameter. The central axis of 
extraneous matter usually consists of a series of single grains, but occasionally we find 
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