518 ARTHUR DENDY. 



tinellida of the "Challenger" Expedition/ 1 to that internal 

 portion of the Sponge body which contains the flagellated 

 chambers, as distinguished from the ectosome, in which, it will 

 be remembered, there are no flagellated chambers at all. 



In Ridleia oviformis the choanosome (fig. 3, ch.) is 

 almost entirely filled up by the closely-packed flagellated 

 chambers which are embedded in a very sparingly developed 

 granular ground-substance, in which it is difficult to make out 

 any cellular constituents. A remarkable character in the 

 choanosome, and to a certain extent in the ectosome also, of 

 the specimen under description, is the occurrence of great 

 numbers of minute, highly refringent, yellowish granules, which, 

 from the fact that they occasionally exhibit a moniliform 

 arrangement, I believe to be bacteria of some description. 

 They are especially abundantly developed around the flagel- 

 lated chambers, and around the inhalant and exhalant cana- 

 liculi. They occur both in stained and unstained preparations, 

 and I am inclined to believe that they were present in the 

 living Sponge. 



The fibrous tissue surrounding the various parts of the canal 

 system has already been described in connection with the 

 similar tissue in the ectosome. 



The Canal System. — The canal system is characterised 

 by its canalicular character, or, in other words, by the absence 

 of irregular lacunse, such as exist in Halichondrine Sponges. 

 The pores (fig. 3, p.) are minute, and scattered apparently 

 without order and rather sparsely over the general surface of 

 the Sponge. They may be seen in sections leading into the 

 narrow, elongated subdermal cavities, which penetrate the 

 various layers of the ectosome and terminate in slightly 

 expanded spaces (subcortical crypts of Sollas) beneath the 

 layer of circular fibres. These subcortical crypts, one of which 

 is shown in fig. 3, are the only portions of the canal system 

 which can be considered as at all lacunar. From them the in- 

 halant canaliculi, leading sooner or later to the flagellated 

 chambers, take their origin. 



1 'Sci. Proc. Roy. Dub. Soc .,' vol. v, pt. vi, p. 177. 



