408 Mr. J. S. Bowerbank on the Spongiadse, 



its production in other and higher orders of the animal king- 

 dom. Thus we find it in the fohated portions of a coral {Pavonia 

 lactuca) when deprived of its earthy matter by dilute hydrochloric 

 acid. In this case, the tissue occurs in the form of shorter and 

 stouter filaments than in the sponge, and there is an attenuation 

 of the fibre towards each of its ends ; nor are the fibres so closely 

 matted together as in the sponges, but on the contrary, there are 

 frequently but a few filaments irregularly disposed amid the de- 

 calcified tissues of the coral. I have also found it in the remains 

 of a fleshy mass of what appeared to be an Ascidian, which was 

 attached to a group of zoophytes from Algoa Bay. It has also 

 been shown, by Dr. Carpenter, that the decalcified shell of the 

 common egg, and its membrana putaminis, are entirely com- 

 posed of this peculiar tissue. In the latter instance the similarity 

 is so great, both in the form of the structure and the mode of 

 disposition, that it would be exceedingly difiicult to distinguish 

 between that derived from the sponge and the tissue of the mem- 

 hrana putaminis^ if it were not that the fibres of the latter are 

 somewhat less in diameter than those of the former. 



The investing membrane is generally exceedingly thin and 

 pellucid, and without any trace of fibres or other forms of or- 

 ganisation. 



Cartilospongia. 



Gen. Char, Fibre cartilaginous, imperforate, containing oat- 

 shaped cavities thickly dispersed, from each of which numerous 

 minute canals radiate to unequal distances. 



C. rigida. Sponge free, compressed, discoid. Fibre rigid, com- 

 pressed ; longitudinal fibres radiating from the centre towards 

 the circumference; lateral fibres at right angles to the longi- 

 tudinal ones, forming square or oblong interstices. Excurrent 

 canals, on the marginal edge of the sponge, few and irregularly 

 disposed. 



The general aspect of the fibre of this sponge is very like that 

 of decalcified foetal human bone from the cranium, but the fibre 

 is somewhat more compressed. 



When a few fibres, immersed in water, are examined by trans- 

 mitted light with a power of 100 linear, it is seen that every 

 part of their substance contains minute oat-shaped cavities, re- 

 presented by PI. XIV. fig. 7, and which correspond exactly, in 

 form and mode of disposition, with the analogous minute cavities, 

 miscalled corpuscles, which abound in such quantities, and are 

 so well known to every anatomist as peculiarly characteristic of 

 true animal bone. In the latter, when viewed with a high micro- 

 scopic power, there may be observed a profusion of exceedingly 

 minute radiating canals, which are said to communicate with the 



