OF THE SPONGIAD^E. 153 



traced in Chalina ocidata, but not to such an extent as in 

 Isodictya palmata. In the sessile massive species of Hali- 

 chondroid sponges the same mode of development seems to 

 obtain, as I have frequently traced the different stages of 

 growth in sections at right angles to the surface of the 

 sponge. 



ON THE CLASSIFICATION OF THE SPONGIAM. 



WHILE the arrangement of other subjects of natural 

 science has occupied the attention of some of the most 

 laborious and talented naturalists of every age, the Spong- 

 iada3 appear to have scarcely attracted sufficient attention to 

 have excited any writer on natural history to a serious 

 attempt at a systematic classification. This neglect has not 

 arisen from any incapacity for a definite arrangement on the 

 part of the Spongiadse, as the organic differential characters 

 of the numerous groups into which, by careful examination, 

 they may be readily divided are as varied and as widely 

 removed from each other as are the strikingly distinct and 

 well defined divisions of the Corallida3, and the number of 

 species I believe to be very much greater than those of the 

 latter class. Of British species alone I am already ac- 

 quainted with more than 150, and new ones are continually 

 being discovered by the aid of the dredge. It becomes 

 therefore a matter of necessity that we should classify their 

 permanent varieties of structure, and found on them a series 

 of orders, suborders and genera, and through these sub- 

 divisions become enabled to recognise more readily the very 

 numerous species of these animals which abound in all parts 

 of the world. 



De Blainville proposed to include the whole of the 

 Spongiadne under the designation of Amorphozoa ; but this 

 term is objectionable, as all sponges cannot be considered 

 as shapeless, on the contrary many genera and species 

 exhibit much constancy in their form. Neither can the 

 term be justly applied to their internal structure, as we find 



