and their Relationshijj to the Corals. 3 



terata, but degraded into the lowest section of the animal 

 kingdom — a particular place being assigned to therii, with the 

 Infusoria and Rhizopoda, among the Protozoa. 



The accurate inves1;igations of the minute organization of 

 the sponges which have been made since 1848, with improved 

 microscopic appliances, and in accordance with the require- 

 ments of modern anatomy, appeared at first to fix this last 

 position afresh. The very careful anatomical investigations 

 of Carter in the East Indies (from 1848) and of Lieberklihn 

 in Berlin (from 1856) seemed concordantly to lead to the re- 

 sult that the sponges were true Protozoa, and possessed close 

 relations of affinity, on the one hand, to the lihizopoda, and 

 especially to the Amoebse, and, on the other, to the true Infu- 

 soria (Ciliata) and to the Flagellata. In particular the struc- 

 ture of the parts of the siliceous skeleton of the siliceous 

 sponges was compared to that of the similar and often 

 scarcely distinguishable siliceous formations of the Sphajrozoa 

 and other Hadiolaria. Moreover certain isolated sponge-cells 

 were not to be distinguished from Amoebge. The isolated 

 ciliary cells from the canal-system of the sponges, which bear 

 only one long whip-like cilium, resembled the individual Fla- 

 gellata, Whilst thus the relationships of the sponges to the 

 other Protozoa were sought in various directions, on the other 

 hand the characteristic canal-system of the sponge-body could 

 not but appear as a higher organic contrivance, Avhich was 

 entirely wanting in the other Protozoa, or at the utmost ad- 

 mitted of a very distant physiological comparison with the 

 conti-actile vesicle of the Infusoria and Amoebae. Hence, in 

 proportion as more extended investigations revealed the multi- 

 farious modifications of this canal-system in the various groups 

 of sponges, the opinion became more and more general that 

 this was a quite peculiar vascular apparatus, and that the 

 whole class of sponges was in consequence to be regarded as 

 a class of animals sui generis^ which stood in no near relations 

 of affinity to any other class, either among the Protozoa or 

 among the Coelenterata. 



This opinon, which is now predominant, that the peculiar 

 canal-system of the sponges represents a perfectly specific 

 nutritive apparatus, such as occurs in no other animals, and 

 that, consequently, the Spongige are to be regarded as a pecu- 

 liar and isolated class of animals sui generis^ was expressed 

 even by Grant (1826) and Johnston (1842), and has been 

 maintained in recent times, especially by those zoologists Avho 

 have gained most credit for the classification of sponges, 

 namely, Oscar Schmidt and Bowerbank. The further the 

 systematic investigations of the latter extended, and the more 



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