Calcispongice in the Animal Kingdom. 247 



any rate only the developmental history and the anatomy of 

 the soft parts could furnish information upon this peculiar 

 structure. It seems rather a bold thing to found an entirely 

 new theory of the organization of sponges upon this skeleton 

 alone, and upon its supposed relationship to the fossil Stroma- 

 topora. In any case this whole theory is completely irrecon- 

 cilable with the facts contained in this monograph. 



3, The Sponges and the Acalephce. 

 In order to recognize the true relationship of the sponges to 

 other groups of animals we must, of course, start from the 

 simplest and least differentiated forms of the class, from Olyn- 

 thus, and from the ArcJiispongia, which differs therefrom by 

 the want of calcareous spicules. When we seek for the nearest 

 relations of these latter in other classes of animals, it is evident 

 that, above all other animals, the simplest forms of the Acale- 

 phan group come into the foreground. But amongst all the 

 known Acalephfe the tw^) freshwater inhabitants of this group, 

 Hydra and Cordyhphora^ are those which exhibit the most 

 primitive conditions of organization, and which must stand 

 nearest to the original stock form of this group. I cannot, 

 therefore, but notice it as an extremely fortunate coincidence 

 that two memoirs have just appeared, which diffuse the clearest 

 light in every direction over these exceedingly important 

 animal forms — namely, the excellent monographs of Hydra by 

 Nicolaus Kleinenberg * and of Gordylophora by Franz Eilhard 

 Schulzef. Both works are admirable in their kind, being 

 distinguished equally by acute observation and by sagacious 

 reflection. The monograph on Gordylophora is perhaps of 

 more importance for our comparison with Olynthus, because 

 this polyp has evidently, in its ontogeny, better preserved the 

 original phylogeny of its ancestors than Hydra^ which is also, 

 in other respects, variously and peculiarly modified in conse- 

 quence of special adaptations. On the other hand, the mono- 

 graph of Hydra is of more importance by reason of the 

 far-reaching philosophical explanations appended to it, and 

 especially of the extremely important reflections upon the 

 germ-lamella theory. Both monographs merit the highest 

 recognition, especially because zoological literature is at present 

 flooded with worthless and unconnected fragments, and on 

 account of the rarity of exhaustive and complete monographic 

 works which furnish a permanent gain to science J. 



* Hydra, eine anatomisch-entwickelungsgescliichtliche Untersuchung. 

 With 4 plates. Ijeipzig, 1872. 



t Ueber deu Ban unci die Entwickehmg von Cordylophora lacustris. 

 With 6 plates. Leipzig, 1871. 



J If I here bring only Hydra and Cordylophora into consideration 

 among the Acalepha3 (the Ccelenterata in the narrower sense), this is 



