ORIGIN OF C(KLOM 297 



Metschnikoff has further the credit of having, in 1874 

 (Zeitsch. wiss. Zoologie, vol. xxiv., p. 15, 1874), revived 

 Leuckart's theory of the relationship of the coelenteric 

 apparatus of the Enterocoela to the digestive canal and 

 body-cavities of the higher animals. Leuckart had in 1848 

 maintained that the alimentary canal and the body-cavity 

 of higher animals were united in one system of cavities in 

 the Enterocoela ( VerwandschaftsverJialtnisse der wirbellosen 

 Thiere, Brunswick, 1848). Metschnikoff insisted upon such 

 a correspondence when comparing the Echinoderm larva, 

 with its still continuous enteron and coelom, to a Ctenophor, 

 with its permanently continuous system of cavities and 

 canals. Kowalevsky, in 1871, showed that the body-cavity 

 of Sagitta was formed by a division of the archenteron into 

 three parallel cavities, and in 1874 demonstrated the same 

 fact for the Brachiopoda. In 1875 (Quart. Journ. Micr. 

 Set., vol. xv., p. 52) Huxley proposed to distinguish three 

 kinds of body-cavity : the schizocoel, formed by the splitting 

 of the mesoblast, as in the chick's blastoderm ; the enteroccel, 

 formed by pouching of the archenteron, as in Echinoderms, 

 Sagitta and Brachiopoda ; and the epiccel. . . . Immediately 

 after this I put forward the theory of the uniformity of 

 origin of the coelom as an enterocoel (Quart. Journ. Micr. Sri., 

 April, 1875). My theory of the ccelom as an enteroccel was 

 accepted by Balfour and was greatly strengthened by his 

 observations on the derivation of both notochord and 

 mesoblastic somites from archenteron in the Elasmobranchs, 

 and by the publication in 1877 by Kowalevsky of his second 

 paper on the development of Amphioxus in which the 

 actual condition which I had supposed to exist in the 

 Vertebrata was shown to occur, namely, the formation of the 

 mesoblast as paired pouches in which a narrow lumen 

 exists, but is practically obliterated on the nipping-off of the 

 pouch from the archenteron, after which process it opens out 

 again as ccelom " (pp. 16-18). 



The enteroccel ic theory was taken up by O. and R. 

 Hertwig as an essential part of their Ccelomtkeorze.^ In 



1 Studien zur Bliitterthcorie, Jena, 1879-80. "Die Coelomtheorie, 

 Versuch einer Erklarung des mittleren Keimblattes,' ; Jenaische Zeitschrift, 

 xv., pp. 1-150, 1882. 



