4 ANATOMY AND PHYSIOLOGY 



and best-known type of the genus, and to refer all others 

 that may distinctly differ from that type to new genera 

 founded on structural principles. 



When I commenced in a similar manner a critical exa- 

 mination of the specific characters of preceding authors, 

 and endeavoured to collect and classify them, I found them 

 to be stiU more indeterminate than those of class or genera ; 

 in truth, it appeared that there was scarcely an approach to 

 a distinct terminology to the science, and that the same 

 author frequently designated the same organ, under dif- 

 ferent circumstances, by a totally different name ; I there- 

 fore felt it absolutely necessary, before proceeding to the 

 description of new species, to enter into a thorough syste- 

 matic examination of the organization of the whole of the 

 species within my reach, and to characterise the organs in 

 such a manner as to render the terms I applied to them 

 definite in their meaning and limited in their application ; 

 and in pursuing this object I quickly found an abundance 

 of constant and well-characterised forms and combinations 

 of organization, capable of being applied with precision to 

 the purposes of generic and specific descriptions. 



I propose, therefore, in the first instance, to characterise 

 the elementary tissues in the following order : 



1. Spicula. 



2. Keratode or homy substance. 



3. Membranous tissues. 



4. Mbrous tissues. 



5. Cellular tissues. 



And, in the second place, to treat of the organization 

 and physiology in the following order : 



1. The skeleton. 



2. The sarcodous system. 



3. The interstitial canals. 



4. Intermarginal cavities. 



5. Dermal membrane. 



6. The pores. 



7. The oscula. 



