CALCAT?EOUS SKELETON OF THE ANTHOZOA. 513 



rest of the spicule exhibits longitudinal striations, more con- 

 spicuous and closer packed together in some places than others, 

 so that the whole section has a banded appearance. In the 

 section figured one may distinguish (1) a medullary portion 

 surrounding the axial diverging lines, which is very finely 

 striated and of a deep pink colour. Outside this is (2) an 

 intermediate portion of lighter substance, coloured a faint 

 pink, and showing few but distinct longitudinal striafions. It 

 should be observed that the intermediate portion ends on the 

 left-hand side of the figure in a blunt point, and that the 

 dark axial lines diverge in a brush-like manner as they ap- 

 proach the point. Both the medullary part, and the inter- 

 mediate part forming the core of the spicule, have the shape 

 and characters of spicules enclosed within spicules, and are 

 without doubt the expression of former stages of growth. 

 (3) The cortical portion, as is shown by its regular longitudinal 

 bands, has clearly been added in successive layers to the inter- 

 mediate portion. It consists of alternately darker and lighter 

 bands, the darker bands being due to the presence of more 

 numerous dark longitudinal striae. The complete correspond- 

 ence between the longitudinal and transverse sections is 

 evident, the concenti'ic laminae of the latter being represented 

 by the longitudinal bands of the former. 



The radiating cords are well exposed in the longitudinal 

 section. It should be noticed that none of them are forked; 

 their bifurcation occurs only in the transverse plane, and 

 cannot be seen in longitudinal section. Each cord starts from 

 the dark axial lines, diverging but slightly from the longitu- 

 dinal axis at firsts but soon turning sharply outwards to run 

 at right angles to the surface, on which it emerges as a warty 

 prominence. A spicule which has been partly ground down 

 and afterwards crushed is seen to be composed of a number of 

 longitudinal fibrous strands, interrupted here and there by the 

 radial cords which traverse them at right angles. Each strand 

 is composed of numerous fibres, which run nearly parallel to 

 one another, and parallel with the long axis of the spicule. 

 Some of these are isolated in a crushed specimen, and each uhen 



