r SjSO Dr Orant's Observations on tlie 



js a necessary result of the kind of basket-work they are em- 

 ployed to construct. The same form of spiculum is met with in 

 the Spongia hispida and S. fruticosa Mont. ; but in the Jruti- 

 cosa it is very short. 



These general forms of silicious spicula are variously modifi- 

 ed in different species of sponge, though they are regular and 

 constant in the same; and there may be many other general 

 forms which have not fallen within my limited observation, or 

 belonging to species yet undiscovered. As the slender vitreous 

 spiculum, acutely acuminated at both ends, is the form met 

 with in the simplest and most irregular of the marine sponges, 

 and also in the fresh- water sponge, a simpler and older zoophyte 

 than any of the marine species (see Ed. Phil. Journ, vol. xiv. 

 p. 283), this spiculum may be considered as the first or simplest 

 in the silicious sponges. It is easy to observe, however, in these 

 sponges, that only one of the acuminated points of the spicula is 

 employed in the defence of the pores and canals, while the other 

 sharp point is fixed and imbedded in the tender substance of 

 the animal, which it is apt to pierce and tear on the slightest 

 motion. The second form of spiculum, therefore, where the 

 unnecessary and probably hurtful imbedded point has been re- 

 moved, either by being simply struck off, as in the S. 'panicea, 

 or by being still further softened by the addition of an enlarged 

 spherical head, as in the S. patera, seems much better adapted 

 for insertion into the soft texture of this animal, or for defending 

 its pores and canals, and probably was of later formation than 

 the preceding form. It is found in some tropical species, and 

 in the Cliona, an animal already possessed of distinct irritability. 

 The numerous inequalities of the waved surface and the round 

 extremity of the third form or jointed spiculum must add to the 

 safety and strength of its attachment to the soft parts ; and the 

 shortness and thickness of this spiculum peculiarly fit it for ward- 

 ing off the assaults of extraneous bodies from the pores of this ani- 

 mal, for which office it seems to be allotted in the specimen before 

 me. It may be supposed, that, at the time of its formation, ani- 

 malcules of a larger magnitude swarmed in the heated ocean ; and 

 this stronger mechanical protection of the pores seems to have been 

 the more necessary, as no animals had yet been formed which 

 could contract and shut their superficial pores by a vital effort like 



