Mr. A. Hancock on the Excavating Sponges* 231 



mounted any of the spicula in balsam ; it was not till some time 

 afterwards that this was done, and the discovery made that a 

 third minute form of spiculum had been overlooked in several 

 of the species. It was unfortunate that this had escaped ob- 

 servation in the first instance, as it aids materially in distin- 

 guishing the species, though the characters originally given 

 appear amply sufficient for the purpose. 



Cliona celata possesses only pin-like spicula, according to all 

 writers on the subject; and it is equally true that most of the 

 Cliona have likewise pin-like forms : but in very many instances 

 they have also associated with them other forms ; and it is such 

 association of various kinds of spicula that chiefly characterizes 

 the species, and that distinguishes most of those I have described 

 from C. celata. Dr. Bowerbank, however, denies the existence 

 of a second kind of spiculum, fusiform or '' acerate," in any of 

 the British species*. This distinguished naturalist believes the 

 fusiform spicula described by me to be adventitious, adhering 

 accidentally to the surface of the sponge. Such belief is per- 

 fectly untenable. The fusiform spicula are not attached to the 

 surface, as assumed by the Doctor, but are imbedded throughout 

 the substance of the sponge in vast numbers ; they are certainly 

 numerically equal to the pin-like form, as is stated to be the 

 case in the original description of C. corallinoides and C. Cana- 

 densis. There is no more reason for supposing the fusiform 

 spicula to be adventitious than there is for assuming the pin- 

 like forms themselves to be so ; both kinds undoubtedly belong 

 to the organism. It may also be stated that numerous foreign 

 species examined by me have similar fusiform spicula associated 

 with the ])in-like form ; and in many instances there is likewise 

 present the third minute kind already mentioned as occurring 

 in several of the British species. But even when only the pin- 

 like spicula are found, they are usually sufficiently characteristic 

 to distinguish the species ; when, however, this form is, as just 

 stated, associated with other kinds of spicula, there can rarely 

 be any doubt on the subject. 



All the three forms of spicula are found in each of the mem- 

 branes of the s])onge. In such species as C Northumhrica, C. coral- 

 linoidesy and C. vastifica the pin-like form is the least numerous, 

 being only sparingly distributed in the internal membranes, 

 though they are densely crowded in the papillae, where they are 

 arranged longitudinally in parallel order, with the heads mostly 

 in one direction ; so that when the papillae are flattened or re- 

 tracted, they assume a radiating disposition. The fusiform 

 spicula are in vast numbers in connexion with the external and 



♦ Op. cit. vol. li. p. 216. 



17* 



