390 



THE MICROSCOPE. 



found in it gemmules still retaining their brown colour 

 and contents capable of development. 



Fig. 214.— Geodia Barretti (Bowerbank). 



A section at right angles to the surface, exhibiting the radial disposition of the 

 fasciculi of the skeleton, and a portion of the dermal crust of the sponge, 

 magnified 50 diameters, a, intermarginal cavities ; b, the basal diaphragms of 

 the intermarginal cavities ; c, imbedded ovaria forming the dermal crust of 

 the sponge ; d, the large patentoternate spicula, the heads of which form the 

 areas, for the valvular bases of the intermarginal cavities ; e, recurvo-ternate 

 defensive and aggressive spicula within the summits of the intercellular 

 spaces of the sponge ; /, portions of the interstitial membranes of the 

 sponge, crowded with minute stellate spicula ; g, portions of the secondary 

 system of external defensive spicula. (1) 



The usual contents of the gemmules have been described 

 by Meyen (Mullers Archiv. 1839, p. 83). In many in- 



(1) See Bowerbank's Monograph of the British Spongiadce, Ray Soc. p. ICO. 



