Upon submitting them to examination with a power of 900 linear, 

 their surfaces were observed to be irregularly tuberculated, as at fig. 

 7, where three of them are seen attached to a fragment of one of the 

 larger spicula of the skeleton, after having been separated by incine- 

 ration from the animal matter that surrounded them. These little 

 spicula, from their great abundance in the encrusted surface of the 

 sponge, are justly entitled to be distinguished as the spicula of the 

 crust. They are found occasionally, but comparatively rarely, along 

 with the stellate spicula of the fleshy substance, and they occur also 

 thinly dispersed beneath the surface of the great excurrent canals. 



I did not succeed in detecting any organization in the epidermal 

 membrane of the crust, probably in consequence of its being obscured 

 by the great abundance of minute spicula immediately beneath its 

 surface ; but in the membrane lining the excurrent canals, there were 

 numerous minute vessels or fibres, disposed in parallel lines, in one 

 part of the tissue, while at another spot they assumed the form of an 

 irregular reticulation. These vessels or fibres are exceedingly mi- 

 nute, and it is requisite that they should be observed with a power of 

 at least 800 linear, and then it is only in the clearest and most trans- 

 parent parts of the membrane that they are likely to be seen. 



The gemmules of this sponge are dispersed, in great abundance, 

 throughout every part of its substance. They are of an oval form, 

 their longest diameter being the ^4-r an d their shortest the ^ T of an 

 inch. They vary considerably in size, but the above are their aver- 

 age dimensions. When seen by direct light, with a power of 100 li- 

 near, they appear of the same colour as the surrounding fleshy matter; 

 but when viewed as transparent objects, they assume an iron or slate 

 grey colour and are nearly opaque, having their surfaces closely stud- 

 ded with minute papillae, which are produced by the projection of the 

 points of numerous small spicula, which are enclosed in the crust or 

 shell of the gemmule, and are disposed in lines radiating from the 

 centre to the circumference of its body. The forms of these minute 

 spicula are exceedingly various, but the best developed ones appear 

 conical, having their bases towards the centre of the gemmule, and 

 their apices slightly elevating the parts of the outer integument im- 

 mediately above them. 



The mode of disposition of these spicula is best observed when a 

 small portion of the sponge has either been treated with boiling nitric 

 acid or by incineration in the flame of a lamp. The dissolution of the 

 gemmules is not effected by either of these agents ; and to view them 

 with the greatest effect they should be gently triturated with a little 



