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DE. J. S. BOWEEBANK ON THE ANATOMY 
3. Multi-spiculated keratose fibre. 
4. Inequi-spiculated keratose fibre. 
5. Simple fistulose keratose fibre. 
6. Compound fistulose keratose fibre. 
7. Regular arenated keratose fibre. 
8. Irregular arenated keratose fibre. 
1. Solid Simple Keratose Fibre. 
The typical form of this description of fibre is that which forms the skeleton of the 
Turkey sponges of commerce, the structure of which I described in a paper read before 
the Microscopical Society of London, and published in vol. i. p. 42 of its ‘ Transactions.’ 
The mature fibre is perfectly solid, and no vestige of a central cavity can be observed in 
any part of it, either when viewed by transmitted light, or in transverse sections of the 
fibre, by the aid of a Lieberkuhn. Occasionally, but very rarely, I have seen, in young 
and immature fibres, faint and irregular indications of there having been a very small 
central cavity in perhaps the earliest period of their development, but in the mature 
fibre I have never been able to trace such cavities (fig. 7, Plate XXVII.). 
This description of fibre is occasionally surrounded by a membranous sheath, on 
which is imbedded a beautiful system of hollow fibrils or vessels, which sometimes ■wind 
round the skeleton-fibre in a spiral direction, at others assume a longitudinal course, 
ghing otf short csecoid branches, or form a complex and irregular network. In an 
Austrahan sponge in my possession, the latter mode is the only form in which they 
occur. In some of these minute fibrils or vessels I observed numerous minute globules, 
which were rendered moveable by a slight pressure on the glass under which they were 
exhibited. The mean diameter of these tubes or vessels was inch. This tissue 
is of rare occurrence, and I have been unable to determine whether it is a specific 
character, or whether it is due to a peculiar condition of the sponge. Fig. 9, Plate 
XXVIII. represents a portion of fibre from the skeleton of one of the sponges of 
commerce. Fig. 10, Plate XXVIII. is from a rigid species of Australian sponge. This 
singular tissue is described more fully in a paper which I read before the Microscopical 
Society of London in 1841, and which is published in their ‘Transactions,’ vol. i. p. 32, 
plate 3. 
2. Spiculated Keratose Fibre. 
This structure is essentially a solid form of keratose fibre, no central cavity ever being 
■visible in its axis. The normal form of the fibre is cylindrical, but it is occasionally 
more or less compressed, and always contains a thin central line or axis of spicula 
an’anged in longitudinal series. The spicula are secreted within the fibre, and are nearly 
uniform in size, and always of the same shape in the same species of sponge. In the 
production of the young fibres, the projection of the new keratode and the secretion of the 
new spicula appear to be simultaneous. In this class of structure the keratose fibre is 
