IM Prof. G. J. Allman on the Anatomy of Actaeon. 



General Observations. 



Such are the facts which, from a most careful examination of 

 a great number of specimens, I beHeve myself justified in consi- 

 dering as demonstrated. I took much pains in again and again 

 verifying their correctness ; and as most of them have not as yet 

 been recorded, while many are in direct variance with recently 

 published statements, I lose no time in making them public. 

 This I am the more desirous of doing, from the fact of the ana- 

 tomy of our little mollusk having within the last year been as- 

 sumed by an acute and indefatigable French zoologist as charac- 

 teristic of a new order of Gasteropoda which he has thought fit 

 to construct, but which appears to me to be constituted upon 

 grounds totally insufficient, in some respects the result of im- 

 perfect observation, and in others of conclusions which the ob- 

 servations, supposing them to be correct, wdl in no degree 

 warrant. 



In the ' Ann. des Sci. Nat.^ 2nde serie, torn, xix., is a memoir 

 by M. de Quatrefages on the anatomy of a small Nudibranchiate 

 Gasteropod, which this naturalist conceives himself justified in 

 separating, imder the name of Eolidinaj from all previously cha- 

 racterized genera of Nudibranchs. In this memoir M. de Qua- 

 trefages maintains, that in the anatomy of Eolidina there are pe- 

 culiarities of such importance as to afford grounds for the esta- 

 blishment of a new order among the Gasteropodous MoUusca. 



M. Milne Edwards had previously directed the attention of 

 zoologists to a remarkable character of the stomach in the Eoli- 

 dian Nudibranchs, demonstrating the existence in Calliopcea of 

 an extensive system of ramified canals connected with this organ. 



Upon this fact M. de Quatrefages seizes with avidity : he main- 

 tains that the gastric ramifications perform the office of branchial 

 vessels ; that they are therefore subservient to respiration as well 

 as to digestion ; and finding them also in his Eolidina, he con- 

 nects them with other peculiarities which he asserts to have dis- 

 covered in this mollusk, raises them to a rank of ordinal import- 

 ance, gives them the name of phlebenteric system, and then sur- 

 prises zoologists with the somewhat startling announcement of 

 the existence of a new order among the Gasteropodous Mol- 

 lusca. 



The doctrines which the examination of M. de Quatrefages^ 

 Eolidina had thus led him to adopt, are carried out to their full 

 extent in a subsequent memoir (Ann. des Sci. Nat. March 1844), 

 in which, after the examination of Actaon and of five new genera 

 of his own characterizing [Zephyrina, Acttsonia, Amphorina, Pelta 

 and Chalidis), he maintains the complete establishment of his 

 new order, and enters into the details of its zoological affinities. 



