200 LIVERPOOL BIOLOGICAL SOCIETY. 



This species is a very interesting one, as from a super- 

 ficial examination with a low power one might think it a 

 ceratose sponge. Even with a high power the spicules 

 are difficult to recognize in the thick ceratose fibres, whilst 

 in other species of Chalina they are seen well with a low 

 power. The thickness of the ceratose fibres is 0*02 to 

 0*075 mm. The spicules are extremely thin oxea, 0'07 by 

 0*002 mm. The width of the ceratose meshes varies from 

 0-15 to 0-30 mm. 



If Lendenfeld* is right in his theory, as he most prob- 

 ably is, that " the skeleton of the Spongidse was developed 

 from that of the Homorrhaphidae by the entire replace- 

 ment of the spicules by spongin," then we must certainly 

 think of forms like Chalina gradient a, which lost the small 

 traces of spicules they still possessed, whilst simultane- 

 ously essential changes in the canal system took place, and 

 thus became changed into Ceratosa. In regard to the 

 changes of the canal system, especially the change of the 

 small flagellated chambers of the Monaxonida into the large 

 sac-shaped ones of the Ceratosa, we may perhaps accept 

 the mechanical explanation which Keller f gives in a recent 

 paper. As a ceratose skeleton has certainly less rigidity 

 than a siliceous one, the flagellated chambers of the Cera- 

 tosa are more liable to become compressed, and to be 

 seriously affected in their function, than those of the silice- 

 ous sponges. An increase in size of the flagellated chambers 

 would therefore be of advantage, as even under pressure 

 some parts of them would remain expanded and functional. 

 Keller's theory accounts well enough for the large flagel- 

 lated chambers of the Ceratosa and Myxospongige, but 

 scarcely for those of the Hexactinellida, which seem to 



* R. V. Lendenfeld, "A Monograj)!! of the Horny Sjwnges," p. 770. 

 + Conrad Keller, "Die S})ongienfauna d. rotlien Meeres." 1. Hiilfte. 

 Zeitsehr. f, wissenscli. Zoologie, 48, Band, 3. und 4. Heft. 



