18C8.] DR. J. S. BOWERBANK ON SPONGES. 135 



name for every part of a sponge we should no more progress suc- 

 cessfully in the description of sponge-species than hotanists would 

 without their copious and well-considered descriptive language. 

 Now I will venture to say that when the terminology relating to the 

 parts of sponges applied in my 'Monograph of British Spongiadse ' 

 has become familiar to the student, he will find no more difficulty 

 in the recognition of a species of sponge described by means of the 

 appropriate technicalities than a botanist encounters when he works 

 out a species of plant that is new to him ; and this is precisely 

 the point at which I have aimed in my sponge-terminology, and 

 by means of which I have described our British species of 

 those animals. I am quite free to acknowledge that in the de- 

 scription of the sponges we are as yet but on the threshold of our 

 structure, and that many new genera must be established to receive 

 the amazing number of exotic species that are still undescribed ; and 

 the most that I can hope for in the course of study that I have 

 shadowed forth in my ' Monograph of the British Spongiadse ' is, that 

 it may prove a sound and useful foundation for the labours of future 

 naturalists in this comparatively untrodden path of zoological science. 

 I shall always hail with pleasure the appearance of new students of 

 these extraordinary creatures, whose labours would advance our 

 knowledge of their structural peculiarities and extraordinary habits ; 

 but amongst this class of students I cannot recognize the author of the 

 singularly loose and impracticable attempt at a systematic arrange- 

 ment of them published in the Society's ' Proceedings' for Mav 1867. 



The essential object of all systematic arrangements is that of 

 arriving with facility and certainty at the knowledge of species by 

 characters common to all the individuals of such groups. This end 

 is not attainable among the Spongiadse by external characters : age, 

 size, colour, and locality modify the external appearances of these 

 animals to so great an extent as to scarcely ever allow of two indi- 

 viduals presenting the same amount of characteristic similarity that 

 is so prevalent among other species of animals. We are therefore 

 driven by necessity to the internal organization to attain the great 

 end of accurate recognition in defiance of all their protean varia- 

 tions in form and colour. 



An accurate and extensive knowledge of species should therefore 

 be our first step towards a scientific arrangement of such animals. 

 As the number of species known to us increases, we quickly find 

 that many of them agree in possessing certain structural characters 

 in common, while each of them has some especial organ which is 

 not existent in the others, and this single peculiarity determines the 

 species ; or it may be that the determinative points may be more 

 than one, or that in place of organs peculiar to certain species, 

 the character may be stamped by other modifications, such as 

 comparative size and peculiar modes of association or disposition of 

 organs common to many species. In any of these cases the deve- 

 lopment of these characters is uniform and certain during all stages 

 of the growth of the individual, and, notwithstanding all other inter- 

 vening difficulties, the discriminationof the species is effective and final. 



