AN IMPORTANT DISCOVERY 



43 



I would wish to lay particular stress upon the composition 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 

 modifications into particular organs, " foundation membranes." 



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

 which he deduces from his observations, is 



That a Medusa consists essentially of two membranes in- 

 closing 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 conception of the 

 affinities of animals. It is the ground on which Haeckel has 

 founded his famous Gastrsea 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. 



