Bibliographical Notices. 53 



titlepage bears, not inappropriately, a woodcut of the little '' chalet" 

 at Wimereux where so much of the work recorded iu its pages has 

 beeu carried on. Throughout the work a number of woodcuts are 

 intercalated in the text, whilst the general illustration of the book 

 is provided for by the beautifully executed plates, in which many of 

 the figures are coloured. We can only hope that MM. (jiard and 

 Bonnier may some day be able to complete their proposed monogra- 

 phic work, and to furnish us with an equally good account of the 

 remaining groups of the Epicarides. 



Freshwater Sponges : a Monograph. By Edwabd Potts. Including 

 'Diagnosis of the European Spongillidjc.' By Prof. Franz Vej- 

 DOTSKY (Prague). Pp. 279, with 12 plates. (Proceedings of the 

 Academy of Natural Sciences, Philadelphia, 1887, p. 157 et seq.) 



Otjr acquaintance with the Sponges has of late years become so 

 extended that they can no longer be regarded by the naturalist with 

 that iudilference which characterized their study when this branch 

 of living beings was only considered for its commercial value. 

 The part which the Spongida have taken, and are still taking, in 

 transforming the invisible into the visible objects of the world has 

 latterly been so realized that to ignore it any longer in failing to 

 direct attention to it seriously would be to disregard the existence 

 of a vast number of living forms which we could or did not care to 

 understand. 



Thus the sponges generally have now become objects of much 

 interest, for they are not only to be found in great abundance living 

 in their natural habitats all over the world, but also, to an almost 

 equal extent, in a fossilized condition ; while lately Dr. G. J. 

 Hinde, F.G.S., has shown that their presence has considerably 

 changed even the composition of whole geological strata by the 

 diffusion of silica which has become liberated from the disintegration 

 of their spicules (Geol. Mag., Oct. 1887, p. 435 &c.). 



Thus the study of the Spongida not only becomes an essential part 

 of biology, but also one of palteoutology and geology. Of course the 

 former led to the latter, as it is mainly by the study of what is 

 taking place at the surface of the earth at the present time that we 

 are enabled to interpret the past. 



As the products of the earth were at first sought after for their 

 direct utility to man, so the species which served that purpose were 

 the first to attract attention ; hence the sponges of commerce have 

 been known from great antiquity, and the most useful ones being 

 marine, those of the sea were the first to be noticed ; but when man 

 began to find that all objects were of interest, if not of indirect 

 vitility, similar ones in freshwater accumulations claimed his notice, 

 and thus from their intimate reserablance he learnt that sponges 

 were to be found in fresh as well as in salt water. 



Latterly many valuable contributions have been made to our 

 knowledge of the Marine Sponge-*, both living and fcssil ; and nu\«r 



