8 A MONOGRAPH OP THE 



The statements of this distinguished anatomist had been far from giving the same 

 satisfaction to naturalists in general that they had done to the commission of the Academy. 

 Their importance, however, had not been overrated ; as, should they prove to be founded in 

 truth, they would have an influence much beyond the dismemberment of a small order of 

 Mollusks, or the establishment of one or two new families. Naturalists had hitherto placed 

 great confidence on deductions drawn from analogy and the correlation of parts. Their 

 experience had shown them that the works of nature exhibited such an uniformity of design 

 as enabled them, from the existence of certain characters, to infer the existence of others with 

 which they had been found to be uniformly associated. Upon such a faith in the constancy 

 of nature, most generalisations are founded. The discoveries of M. de Quatrefages tended to 

 shake this confidence, and to vitiate in future all arguments drawn from analogy. It was not 

 to be wondered at, therefore, that his statements were received with mistrust, and the supposed 

 facts submitted to a rigorous scrutiny. 



Among the foremost to oppose these views was M. Souleyet. In a communication to the 

 Academy of Sciences,* this naturalist expresses his conviction, founded upon a careful 

 anatomical investigation, that the so called gastro-vascular apparatus was no other than a 

 system of highly developed biliary ducts, rendered necessary by the dismemberment of the 

 liver in these animals. Rejecting, therefore, the idea of the union of functions assigned to 

 them, he proposed to call these vessels gastro-biliary. He demonstrated, from the anatomy of 

 Eolis, between which genus and Eolidina he could see no essential difference, that the marginal 

 canal described by M. de Quatrefages, and considered by him analogous to that of the 

 Medusas, did not exist, and further asserted that in Eolis the vascular system was not less 

 perfect than in the other Mollusca. No degradation from the usual type of the class was 

 therefore to be found in the animals examined. 



In a Report to the British Association for the Advancement of Science, in 1844, we again 

 objected to most of the opinions of M. de Quatrefages on this subject. And in the first part 

 of a paper on the anatomy of Eolis,f published in 1845, Mr; Hancock and Dr. Embleton 

 pointed out several errors of detail in that gentleman's memoirs. They there take the same 

 view of the gastro-vascular system as that expressed by M. Souleyet. 



Subsequently, M. de Quatrefages entered into a general exposition of his views on the 

 organisation and arrangement of the animal kingdom, showing that with these his observations 

 on the anatomy of the Mollusca perfectly agreed. In conformity with the views of Professor 

 Milne Edwards, he contends for a plurality of series in the animal kingdom, and the degradation 

 of many of them ; and he further states that, in numerous instances, the general form of the 

 body and the internal organisation are perfectly independent of each other. Phlebenterism, 

 he says, is not confined to the Mollusca : " It exists in the animal kingdom taken as a whole, 

 and in many of the secondary and tertiary series which concur to form it. Nearly throughout, 

 we see it coincide with the manifest degradation of the entire organisation. Almost always 

 it coincides with the simplification or complete annihilation of the organs of circulation." % 



The observations of M. Souleyet, in reply to those of M. de Quatrefages, were, for the most 

 part, directed to the two principal points in dispute; namely,— the function of the branched 



* 'Comptes Kendus/ v. 19, p. 355 (1844). f 'Ann. Nat. Hist./ v. 15, pp. ], 77. 



t ' Comptes Eendus/ v. 19, p. 809. 



