36 ANATOMY AND PHYSIOLOGY 



the spicula appearing to be destined to wound and lacerate, 

 rather than to retain intruding enemies, while a larger 

 and stronger series of spicular weapons bear all the 

 evidences of being to retain rather than to repel the 

 assailants. 



The first description of spiculum I have designated 

 entirely spined, spiculated cruciform spicula. They con- 

 sist of a short stout cruciform base with a long spicular 

 ray, ascendingly and entirely spinous, projected at right 

 angles from the centre of the basal radii. The spines are 

 acutely conical, and very sharply pointed. They pass off 

 from the spicula ray at an angle of 12 or 15 degrees in 

 the direction of its apex. The apices of the basal radii 

 are attenuated and slightly spined. These spicula are 

 thickly distributed on the fasciculi of the skeleton, and 

 frequently equally so on one side of the interstitial 

 membranes, probably that which forms the surfaces of the 

 interstitial spaces, and they are especially abundant near 

 the exterior of the sponge. The four basal radii appear 

 firmly cemented to the membrane, but not immersed in 

 its substance, as they do not appear to leave their impres- 

 sions when removed from it, nor do they bring any portion 

 of the membrane away with them. In some parts of the 

 tissue these spicula are very much modified in form. In 

 the ordinary cases we find the basal radii short and stout, 

 and not more than a fourth or a fifth of the length of the 

 spicular ray, while in other cases the basal rays are very 

 nearly as long as the spicular one; the only difference 

 in their structure being that the latter is very strongly 

 spinous, while the former have the spines comparatively: 

 very slightly produced. 



The second form is a large fimbriated multihamate 

 birotulate spiculum, which occurs dispersed amid the 

 interstitial tissues of the large basal mass of the sponge. 

 There are usually not more than one or two together, but 

 occasionally they occur in groups of ten or twelve, without 

 any approach to definite arrangement. 



These spicula are comparatively large and stout. They 

 have eight rays at each end of the shaft ; the two groups of 



