M. DE QUATREFAGES. 595 



of the genera that came under his investigation are models 

 for posterity to imitate, perhaps not to excel. Yet his 

 countrymen have rivalled him ; and from the admirable 

 essays of M. de Quatrefages, Souleyet, Milne-Edwards, 

 and Emile Blanchard, we might learn nearly all that is yet 

 known of the order in an anatomical and physiological view. 



M. de Quatrefages, in 1844, proposed to detach from the 

 Nudibranches a considerable tribe, and with it to establish a 

 new order amongst the Gasteropoda, distinguished by the 

 inferiority or degradation of their structure. In the Eolidina 

 he asserted that the circulatory apparatus was reduced to a 

 heart and arterial vessels only, the veins having disappeared, 

 and with them the respiratory organs. These were replaced 

 by an intestinal tube which not merely separated from the 

 food a chyle fit to enrich anew the impoverished blood, but 

 further acted on it and prepared it for assimilation with the 

 body, performing in fact the duty of the respiratory function. 

 In the Zephyrina, in Acteon and Acteonina, the heart, 

 which, in the Eolidina, fulfilled no other function than as an 

 agent of mixture " Ne remplissait plus que les fonctions 

 d'un agent de melange," disappears, and with it the entire 

 circulating system. The alimentary tube, however, now 

 becomes even more ramose than it is in the Eolidina, and we 

 can detect movements in it which remind us of the pulsations 

 of a heart. The function of respiration seems also to be 

 entirely devolved on other structures, more especially on 

 the skin ; and the purification of the vital fluid is no longer 

 localized in the dorsal filaments. In the Amphorina we see 

 the intestinal ramifications again diminish in number while 

 they increase in size, a modification of the structure which 

 imposes on the skin an increasing share in the respiratory pro- 

 cess ; but as there still exist exterior appendages into which 

 no intestine penetrates, so whatever may be the importance 

 of the integuments in respiration, the function is not effected 

 by them unassisted. But in the genus Pelta, and in the 

 Chalides, every exterior appendage has disappeared ; the in- 

 testine has seemingly become concentrated into one or two 

 great pouches, which probably act with feebleness, and 

 secondarily only in respiration ; and the skin alone has de- 

 volved upon it the duty of that important office. 



From this transference of the function by which all ani- 

 mated beings breathe and live, from the gills to the intes- 

 tinal canal and to the skin, and which is accompanied with 

 other modifications of the organization irreconcilable with 

 the usual character of their class, M. de Quatrefages has 

 proposed to remove the Eolidina, and the allied genera, to a 



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