194 ANATOMY AND PHYSIOLOGY 



and the older authors, and therefore the proper type of the 

 genus, we find the skeleton destitute of fibre, but composed 

 of an irregular network of spicula cemented together at their 

 apices by keratode. If we examine the well-known branching 

 sponge so common on all our coasts, Halichondria oculata 

 of the same author, we find an abundance of keratose fibre 

 containing spicula deeply imbedded in its substance, but 

 not necessarily uniting at their apices, and the network of 

 the skeleton is not irregular as in the first instance, but on 

 the contrary is more or less symmetrically disposed in all 

 parts of the sponge. If we take Halichondria suberea of 

 the same authors we find neither network of spicula nor a 

 keratose fibrous structure, but apparently an amorphous 

 sarcoid mass containing spicula and membranes, on which 

 the former are dispersed without any order or connection. 

 As we extend our researches among the other British 

 species of Fleming's genus Halichondria, other striking 

 and permanent variations in the arrangement of their 

 skeleton tissues present themselves. Their great differences 

 in structure therefore afford ample grounds for the division 

 of the species comprehended under Halichondria as consti- 

 tuted by Fleming into a series of genera, having each for 

 its base a separate type of organization ; and as the vari- 

 ations in structural character, some of which are mentioned 

 above, are both numerous and strikingly characteristic, I 

 propose to limit the genus Halichondria to those species 

 only, which agree in their organization with H. panicea of 

 Johnston, and to distribute the remaining species in other 

 genera, the distinctive characters being in all cases based 

 primarily on the different modes of the organization of the 

 skeleton of the animal, and when necessary taking in aid 

 such other organic characters as may be found available for 

 the purpose of accurate discrimination. I therefore propose 

 to limit the genus Halichondria to those sponges only, that 

 exhibit the following characters. 



