OF THE SPONGIAD^. 341 



Fig. 



the intermediate gradations of development may be 



observed among the spicula of young specimens of 



the sponge. The two figures are drawn by the same 



power, 260 linear, and the difference in size between 



the young and the fully-developed spiculum is very 



remarkable. 



This form is both defensive and retentive, internally 



and externally. See Mg. 354e, Plate XXVIII, and 



Pig. 362 c, Plate XXXI. 



83. Attenuato-tClavate : incipiently spined. — The 



enlargement of the base of this spiculum is not 

 spherical as in a spinulate form, but it expands more 

 or less gradually and is usually exaxiaJ. They are 

 projected in abundance into all parts of the inter- 

 stitial cavities of Hymeniacidon davigera. Bower- 

 bank. X 130 linear. 



84. Equiangular triradiate : verticillately spined. 



— This beautiful spiculum was found among 

 minute fragments of various sponges scraped from 

 the bases of specimens of Oculina rosea. I have 

 not hitherto found vertieiUately spined sponge 

 spicula imder any other character than that of de- 

 fensive spicula, and I have therefore arranged this 

 one as such until further information shall be ob- 

 tained regarding it. X 400 linear, 



85. Ensieorm spiculated equiangulated triradiate. 



— The spicular ray is at right angles to the com- 

 mon plane of the basal radii, but not of the same 

 form. It is very much longer and stouter than 

 the basal radii, and its diameter is considerably 

 increased in the distal third. Internal defensive. 

 X 130 linear. Erom the cloaca of Grantia ensata, 

 Bowerbank. Page 29. 



86. A variety of the same form of spiculum as that repre- 



sented hy Pig. 85. Erom the cloaca of Grantia 

 tessellata, Bowerbank. X 130 linear. See Eig. 

 286, Plate XVII, in situ. Page 29. 



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