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 4. 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 : — 
7. The oscula, 
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 
8. Inhalation and exhalation, 
9. Nutrition, 
10. Cilia, and ciliary action, 
11. Reproduction, gemmules,&c. : 
The generic characters, 
The specific characters, and 
On the method of examination. 
This is the outline of a comprehensive and scientific 
