238 Proceedings of the Royal Physical Society. 



skeleton which exists in that species of sponge which is the 

 oldest established and best known type of the genus, and 

 refers all others that may distinctly differ from that type to 

 new genera founded on structural principles. When Dr 

 Bowerbank commenced, in like manner, a critical examina- 

 tion of the specific characters of preceding authors, and 

 endeavoured to collect and classify them, he found them to 

 be still more indeterminate than those of class or genera ; it 

 appeared to him that there was scarcely an approach to a 

 distinct terminology of the science, and that the same author 

 frequently designated the same organ, under different cir- 

 cumstances, by a totally different name. He therefore felt it 

 absolutely necessary, before proceeding to the description of 

 new species, to enter into a thorough systematic examina- 

 tion of the organisation of the whole of the species within 

 his reach, and to characterise the organs in such a manner 

 as to render the terms he applied to them definite in their 

 meaning, and limited in their application ; and in pursuing 

 that object he quickly found abundance of constant and 

 well characterised forms and combinations of organisation 

 capable of being applied with precision to the purposes of 

 generic and specific descriptions." 



He therefore proposes to characterise the elementary 

 tissues in the following order :— 



1. Spicula, I 4t. Fibrous tissues, 



2. Keratode, or horny substance, 5. Cellular tissues, 



3. Membranous tissues, ' 6. Sarcode ; 



And to treat of the organisation and physiology as fol- 

 lows : — 



1. The skeleton, 



2. The sarcodous system, 



3. The interstitial canals, 



4. The intermarginal cavities, 



5. Dermal membrane, 



6. The pores, 



And to conclude with observations on 



7. The oscula, 



8. Inhalation and exhalation, 



9. Nutrition, 



10. Cilia, and ciliary action, 



1 1 . Reproduction , gemmules, & c . ; 



The generic characters, 

 The specific characters, and 

 On the method of examination. 



This is the outline of a comprehensive and scientific 



