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Show 1868.] DR. J. S. BOWERBANK ON SPONGES. 135 name for every part of a sponge we should no more progress successfully in the description of sponge-species than botanists would without their copious and well-considered descriptive language. N o w I will venture to say that when the terminology relating to the parts of sponges applied in m y ' 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 m y 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 description 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 m y ' 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 arrangement of them published in the Society's ' Proceedings' for M a y 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 individuals presenting the same amount of characteristic similarity that is so prevalent among other species of animals. W e are therefore driven by necessity to the internal organization to attain the great end of accurate recognition in defiance of all their protean variations 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 development of these characters is uniform and certain during all stages of the growth of the individual, and, notwithstanding all other intervening difficulties, the discrimination of the species is effective and final. |