OF THE SPONGIAD^E. 37 



radii curving towards each other to such an extent that 

 each forms the half of a regular oval figure ; the opposite 

 apices being separated to the extent of about the length of 

 one of the radii. Each ray is in form like a double-edged 

 blunt-pointed knife, bent near the handle in the direction 

 of a line at right angles to one of its flat sides ; and each 

 ray is strengthened and connected with the shaft of the 

 spiculum by a stout curved web of silex, which extends 

 from a little below the inner surface of the ray to a point 

 on the shaft about opposite to its middle. The shaft is 

 cylindrical, and has short stout tubercles dispersed over all 

 its parts when fully developed. 



The structure of every part of this singularly beautiful 

 spiculum is strikingly indicative of its office in the economy 

 of the sponge ; the form and mode of bending of the radii, 

 with their thin edges at right angles to the line of force in 

 a struggling animal, and the powerful web at the base of 

 the ray enabling it to sustain an amount of stress that the 

 unsupported flat ray would never otherwise be able to endure. 



The spiculated cruciform spicula are exceedingly 

 abundant in every part of the sponge, and no victim 

 entangled and retained by the large multihamate spicula 

 could avoid innumerable wounds while struggling to effect 

 its escape ; while the one held it secure within the sponge, 

 the others, from the peculiarity of their form and mode of 

 the disposition of their acutely pointed spines, would 

 readily release it after the infliction of every puncture, 

 only that the wounds might be multiplied until the 

 creature was pierced in every part, and bled to death for 

 the nutrition of the sponge. 



Tig. 294, Plate XVIII, represents a small portion of 

 the skeleton of Ihe sponge with the two forms of defensive 

 and aggressive spicula in situ, magnified 50 linear. Fig. 

 60, Plate III, represents one of the multihamate bihamate 

 spicula with a power of 83 linear, displaying the adap- 

 tation of its structure to purposes of retention. Fig. 

 295, Plate XVIII, represents one of the spiculated cruci- 

 form spicula magnified 175 linear, on the same scale as 

 Fig. 60, Plate III, showing their relative proportions. 



