56 ANATOMY AND PHYSIOLOGY 



the base, and then it again curves outward, until the 

 apical expansion is at right angles to the floral axis ; so 

 that the whole resolves itself into a form like that of the 

 flower of a Jasmin. The beautiful terminal petaloid 

 expansions, with their regularly disposed marginal dents, 

 renders the illusion complete ; the united basal curves 

 looking as if they had been produced by the swelling 

 ovarium of a flower. 



I have obtained a considerable number of these elegant 

 spicula from my friend Mr. Cuming's beautiful specimen of 

 Euplectella aspergillum, Owen, which, with his accustomed 

 liberality, he placed at my disposal for examination. They 

 are found also in Dr. A. Farre's specimen of Euplectella 

 cucumer, Owen, agreeing in every respect with those from 

 Mr. Cuming's sponge. 



Generally speaking, the slender rectangulated hexradiate 

 spicula occur singly, but I have sometimes found them 

 grouped together; in this case their axes were coincident 

 and their radii in the same plane, or very nearly so, but not 

 always agreeing in their direction ; such a framework would 

 form a very fitting support to a large mass of sarcodous 

 tissue partially separated from the framework of the skeleton 

 and occupying a portion of a large interstitial space. 



In the large open areas of the skeleton of Euplectella 

 aspergillum, Owen, the hexradiate forms, ranging from 

 Figs. 174 183, Plate VII, are exceedingly abundant, and 

 a considerable number of them are not developed to 

 the extent of the full number of their radii. This mav 



i/ 



probably arise from the development of the radii being 

 stimulated bv the necessities of the mass of sarcodous 



V 



tissues in which they are imbedded, and consequently 

 where no necessity for their presence exists they would 

 not be put forth. In the trifurcate and quadrifurcate 

 hexradiate forms, if we may judge from the termination 

 of their radii, they, like the simple stellate forms, are either 

 purely consolidating, or they combine with that office that 

 of defensive spicula also, as far as regards the sarcodous 

 substance in which they are imbedded. 



We can scarcely imagine any defensive properties in the 



