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XXXII. On the Anatomy and Physiology of the Spongiadce. — Part II. 
By J. S. Boweebank, LL.D., F.B.S., F.L.S. &c. 
Eeceired June 17, — Eead June 20, 1861 (continued from page 332, Philosophical Transactions, 1858). 
Keratode 
Is the substance of which the horny elastic fibres of the skeleton of the officinal sponges 
of commerce are composed. It has, correctly speaking, no relationship either chemically 
or structurally with horn, and Dr. Geant has judiciously rejected the term “ horny fibre” 
as applied to the sponges of commerce, and has substituted that of keratose by way of 
distinction; and in accordance with that term I propose to designate the substance 
generally as keratode, whether it occurs in the elastic fibrous skeleton of true Spongia^ 
which are composed almost entirely of this substance, or of those of the Halichondraceous 
tribe of Spongiadae, where it is subordinate to the spicula in the construction of the 
skeleton, and appears more especially in the form of an elastic cementing medium. In 
a dried state it is often extremely rigid and incompressible, but in its natural condition 
it is more or less soft, and always flexible and very elastic. It varies in colour from a 
very light shade to an extremely deep tint of amber, and it is always more or less trans- 
parent. In its fully developed condition, in the form of fibre, it appears always to be 
deposited in concentric layers ; but in the mode of the development of these layers there 
are some interesting variations from the normal course of production. As we And in 
Aranea diadema, the common Garden Spider, that the creature has the power of modi- 
fying the deposit of the substance of its web so that the radiating fibres dry rapidly while 
the concentric ones remain viscid for a considerable period, so we And in the production 
of the young fibres of the skeletons of the Spongiadse in some species, as in those of 
commerce, there is no adherent power at the apex of the young fibre, excepting with 
parts of its own substance ; while in Dysidea, and in some other genera, the apex of the 
newly-produced fibre is remarkably viscid, adhering with great tenacity to any small 
extraneous granules that it may happen to touch in the course of its extension ; but this 
adhesive character appears to be confined to the earliest stages of its production only, 
as exhibited at the apices of the newly-produced fibres, the external surface immediately 
below the apex exhibiting no subsequent adhesive property. 
Lehman, in his ‘ Physiological Chemistry,’ Cavendish Society’s edition, vol. i. p. 401, 
states that Spongia officinalis of commerce consists of 20 atoms of fibroin, 1 atom of 
iodine, and 5 atoms of phosphorus ; and in treating of the physiological relations of 
fibroin as regards sponges, he observes, “ Its chemical constitution afibrds one of the 
arguments why the Spongia should be classed among animals and not among plants, 
MDCCCLXII. 5 K 
