256 ANATOMY AND PHYSIOLOGY 



FIG. 



sents, about the first stage of variation from the 

 simple elongate spinous spiculum, a few rather 

 strongly produced cylindrical spines appearing near 

 the middle of the shaft. In Fig. 169, two of these 

 spines are considerably more elongated than those 

 in Fig. 168, and the shaft is not so long as in that 

 figure. In Fig. 170 the axial shaft is still more 

 curtailed in its proportions, and the central radii 

 are further elongated and increased in number; 

 and in Fig. 171 we find the axial spiculum scarcely 

 distinguishable from the lateral rays. When the 

 radii projected are few in number, they are usually 

 at right angles to the axial spiculum. ; but when 

 they are produced in greater numbers, they are 

 projected at various angles, and the axial spiculum 

 can scarcely be detected. In spicula having numer- 

 ous radii, they frequently unite at their bases, and 

 produce their extreme variation of form, a sub- 

 sphero-stellate spiculum. No two of these singular 

 spicula are alike, and they present every imaginable 

 variation in the mode of their development. In 

 their origin from an axial spiculum, and in their 

 tendency to the projection of secondary radii at 

 right angles to that axis, these spicula form a con- 

 necting link between the simple multiradiate forms 

 and the more complicated ones belonging to the 

 compound stellate spicula. 



172. EXTER-SPINULATED ARCUATE. X 1250 linear. From 



a small, massive sponge from the Bahamas, pre- 

 sented to me by my friend Mr. McAndrew. They 

 are very abundantly dispersed over all parts of the 

 interstitial membranes, are uniform in size, and 

 vary to some extent in the degree of spiculation. 



173. SUBSPINULATO-ARCUATE. 260 linear. Abundantly 



dispersed on the interstitial membranes of a new 

 species of sponge from Freernantle, Western Aus- 

 tralia ; sent to me by my friend Mr. Geo. Clifton. 



