Siliceous Spicules of Sponges. 207 



by which they are attached more or less distorted, and have 

 the parts well developed which are at the free extremity, like 

 those free in the sarcode. Dr. Bowerbank calls the free form 

 " equianchorate," and the attached spicule " inequianchorate." 

 They are very abundant in their most perfect form; they 

 occur free in the flesh of the sponges. 



The most perfectly developed spicule of this form has three 

 well-developed spreading lobes at each end, all on the same 

 side. 



The stem between the lobes is cylindrical, more or less 

 arched (B. S. t. vi. f. 140, " tridentate equianchorate spicule," 

 and t. vi. f. 141-149) &c. 



Sometimes the part of the stem between the hooks is dilated 

 on the sides, as in B. S. t. vi. f. 150. For the attached or in- 

 equianchorate spicules of this form see B. S. t. vi. f. 135-137, 

 142, 146, 148. 



Sometimes the end of the spicule is more or less expanded, 

 and only the central lobe or spine is developed : B. S. t. vi. 

 f. 138, with the central stem rather elongate and the expan- 

 sion half-ovate ; B. S. t. vi. f. 139, with the expanded ends 

 half-oblong and the intermediate slenderer portion compara- 

 tively short. 



Sometimes the spicule is very slender and only recurved at 

 the end, as in B. S. t. vi. f. 144, 145. Indeed one would not 

 believe that they belonged to this series ; but in B. S. fig. 145 

 there is a slight dilatation on each side below the hook, and 

 fig. 146 is intermediate in form between them and the more 

 typical hamate spicule. See Carter, Ann. & Mag. N. H. 1871, 

 viii. t. iv. f. 8 ; 1872, ix. t. x. f. 5. 



Many of the spicules of this series are not so perfectly deve- 

 loped, being much more simple, subcylindrical, unilateral, with 

 recurved ends. In one, the ends are longer, recurved, sharp- 

 edged on the inner side (see B. S. t. v. f. 112, "trenchant 

 contort bihamate "). 



Others are cylindrical in the body ; and Bowerbank calls 

 them "simple hamate spicules" (B. S. t. v. f. 109, 114). 

 These spicules sometimes have the terminal hooks turned in 

 opposite directions, forming an S, thus losing their unilateral 

 character; but this is only a malformation (B. S. t. v. f. 110, 

 111). They have a close resemblance to the least-developed 

 bihamate spicule, figured in B. S. t. vi. f. 144, referred to 

 above, showing the passage of the two forms of spicule into 

 one another. Some of these more slender spicules have a pro- 

 minence or knob on the middle of the inner side of the body 

 (B. S. t. v. f. 116), some on the middle of the outer side (B. S. 

 t. v. f. 115), and some on both the inner and outer sides (B. S. 



15* 



