IV.-CONCLUDING REMARKS. 



With the last lines of the foregoing chapter the direct and immediate task of this 

 memoir is accomplished, but it remains still to summarise its more general deductions 

 with respect to what I regard as its chief purpose. The tendency of this is to clear up 

 the present state of our knowledge, and in the first place to prove that, in spite of the 

 acquirement of many new systematically important characters introduced into descriptive 

 Spongiology by F. E. Schulze, which concern the peculiarities of the internal organisation 

 of the soft parts, all the arrangements of the Keratosa hitherto proposed are, on 

 the whole, far from being natural. I hope I have made it clear that the procedure 

 of subdividing the group either directly into families or preliminarily into suborders may 

 be adopted merely as a measure of provisional character. I hope I have also proved 

 that the genera established in the Keratosa are not homogeneous, the characters dis- 

 tinguishing one part of them being of an absolute, those distinguishing another part of 

 an extremely conditional, and often very ambiguous, nature. I am, finally, far from any 

 illusions, and feel certain that the perusal of the descriptive part of this memoir, as well 

 as of other systematic papers on the Keratosa, must show plainly that in most cases the 

 classifier has to found his species on characters whose stabiUty is quite unknown to him, 

 so that whether they are really of specific importance or fit only for distinction of indi- 

 viduals, remains open to discussion. The reader sees that the state of matters is far from 

 satisfactory; and it is natural to ask whether it admits at least of some conjectures as to 

 the way in which our knowledge of the Keratosa may become more perfect ? I believe 

 this question may be answered in the affirmative ; but since, in cases where decisive, 

 incontestable proofs are wanting, the probability of the suggestion depends on the 

 number of arguments, I should like, before I pass on to the recapitulation of the grounds 

 favourable to my opinion, to increase their number by an argument of no little consequence. 

 This argument refers to the systematic position of the Keratosa in the whole group of 

 Porifera, and it appears to me that a detailed discussion of this question will be the 

 less superfluous, as the corresponding conclusions promise to be not only of theoretical 

 importance but also of practical applicability. There are mainly in practice two different 

 methods of systematic procedure. The usual one is to begin with lower systematic 

 unities, in order to ascend to families, orders, &c. With respect to many other instances 



