388 HISTORY OF GEOLOGY AND PALAEONTOLOGY. 



material for microscopic examination. In 1877, Sollas demon- 

 strated, by his examination of several genera belonging to the 

 English chalk, the identity of their structure with that of living 

 hexactinellids, lithistids, and monactinellids. Zittel, in 1876, 

 published his microscopic investigations embracing the whole 

 of the fossil sponges, together with a monograph of the genus 

 Coeloptychium. In this work, as well as in the studies 

 published during the following year, it was fully demonstrated 

 that all fossil sponges could be included in the scheme of 

 classification erected for existing sponges. Zittel succeeded in 

 showing that a large number of sponges referred to the Calci- 

 spongiaa by previous authors had been originally arenaceous, 

 but the sandy material had been dissolved, and in its place 

 calcareous substance had been laid down. This removed the 

 greatest difficulty in the study of fossil representatives of the 

 Silicispongiae. Zittel also demonstrated the true calcareous 

 structures of numerous fossil Calcispongiae, whose existence 

 had been called in question by E. Haeckel in his monograph of 

 the Calcispongiae (1872), and in spite of much contradiction at 

 first, Zittel's evidence ultimately received general acceptance. 



The application of the microscopic method, which had been 

 used by Zittel and Sollas, was followed in almost all the later 

 publications on fossil sponges, and the classification proposed 

 by Zittel for recent and fossil sponges was confirmed in its 

 main features and further improved by the zoological and 

 anatomical investigations of O. Schmidt, F. E. Schulze, Carter, 

 Vosmaer, Lendenfeld, and others. 



The most distinguished students of fossil sponges at the 

 present day are G. J. Hinde and Hermann RaufT. The former 

 has published a monograph of the fossil sponges (1884) in the 

 Natural History Collection of the British Museum, and is at 

 present engaged on a monograph of the fossil forms of Great 

 Britain, parts of which have appeared since 1887 in the 

 publications of the Palaeontographical Society. Kauff has 

 produced in his Palceospongiology (1893) an exemplary repre- 

 sentation of all the palaeozoic forms of sponges. 



C&hnterates. Up to the year 1825 there was great in- 

 security about the organisation of the organisms at present 

 comprised under the group of the Coelentera. The schemes of 

 classification attempted by Lamouroux, Esper, Lamarck, and 

 others are full of errors; the researches of Ehrenberg and 



