216 On the Siliceous Spicules of Sponges. 



the siliceous spicules of other sponges, but seem to be modi- 

 fications of the horny skeleton of the Aply since and other 

 horny sponges, as Mr. Carter considers them. They differ from 

 spicules in their mode of development, their structure, form, 

 and the manner in which they adhere together; indeed it 

 would hardly occur to any one but a theorizing German to 

 regard them as such. 



The results of this paper may be thus epitomized : — 



1. Needle-like spicules. 



a. Cylindrical. 



b. Tapering at each end. 



c. Tapering at one end. 



d. Club-shaped. 



e. With a head at one end. Sometimes this head is 



double or treble. 



f. With a head at each end. 



g. With a thick belt in the middle. 



Each of these is straight or sinuous, has the surface smooth, 

 tubercular, or spinulose, the tubercles or spines being some- 

 times scattered, at others placed in whorls. 



2. Hamate spicules. 



a. The ends dilated and divided into three acute pro- 



cesses ; but sometimes the lateral processes are 

 wanting. When free in the sarcode, both ends are 

 equally dilated; when attached in groups, the 

 attached end is only imperfectly developed. 



b. The spicules compressed, with a sharp edge at each 



end. 



c. The spicule more or less cylindrical, curved at each 



end. These spicules are sometimes bent like an 

 s, at others only slightly doubly curved or nearly 

 straight. 



3. Quinqueradiate. 



a. Spicules with the axis very long and the rays 



tapering and sometimes forked. 



b. Axis very short, the rays elongate, slender, forked, 



or expanded into a broad, circular or more or less 

 lobulated disk. 



Bowerbank figures some spicules which appear to belong to 

 this division, without any axis ; but I have not had the op- 

 portunity of seeing them. 



