58 LIFE OF PROFESSOR HUXLEY CHAP. Ill 



ticular genera and species." At the outset, section 

 8 (Sci. Mem. i. 11), he states 



I would wish to lay particular stress upon the com- 

 position of this (the stomach) and other organs of the 

 Medusae out of two distinct membranes, as I believe that it 

 is one of the essential peculiarities of their structure, and 

 that a knowledge of the fact is of great importance in 

 investigating their homologies. I will call these two 

 membranes as such, and independently of any modifica- 

 tions into particular organs, " foundation membranes." 



And in section 56 (p. 23) one of the general con- 

 clusions which he deduces from his observations, is 



That a Medusa consists essentially of two membranes 

 inclosing a variously -shaped cavity, inasmuch as its 

 various organs are so composed, 



a peculiarity shared by certain other families of 

 zoophytes. This is the point which that eminent 

 authority, Professor G-. J. Allman, had in his mind 

 when he wrote to call my attention 



to a fact which has been overlooked in all the notices I 

 have seen, and which I regard as one of the greatest 

 claims of his splendid work on the recognition of 

 zoologists. I refer to his discovery that the body of the 

 Medusae is essentially composed of two membranes, an 

 outer and an inner, and his recognition of these as the 

 homologues of the two primary germinal leaflets in the 

 vertebrate embryo. Now this discovery stands at the 

 very basis of a philosophic zoology, and of a true concep- 

 tion of the affinities of animals. It is the ground on 

 which Haeckel has founded his famous Gastraea Theory, 

 and without it Kowalesky could never have announced 

 his great discovery of the affinity of the Ascidians and 

 Vertebrates, by which zoologists had been startled. 



