598 



HISTORY OF SYSTEMS. 



This view of the function of the organ was taken by Soule- 

 yet, and is now acquiesced in by all comparative anatomists, 

 so that it affords an unexceptionable basis for divisions of a 

 secondary rank, provided it is accompanied with " outward 

 observances" that may disclose the secret structure to the 

 zoologist, who rightfully demands that his index to the beings 

 he searches out shall be made patent to his senses without 

 calling to their aid the knife of the anatomist. Internal 

 structures unrevealed by external marks, are not admissible 

 in classifications ; but in the present case there is no room 

 for cavil. Professor Allman has exhibited his views in the 

 following neat table : — 



Order, 



I 



Section. 



Liver compact. ( 



1 



< 



n 

 a 



Liver disintegra- « 

 ted. 



Family. 



Branchiae in the mesial line, placed 

 in a circle more or less complete 

 around the anus. 



DORIDID.E. 



Branchiae arranged along the sides, 

 or scattered. 



Tritoniadje. 



Branchiae papillose, or branched, or 

 muricated. 



Eolidid-s:. 



Genus. 



.Doris, Polycera, 

 &c. 



. Tritonia, Scyllaea, 

 Thetis. 



\ 



Branchiae foliaceous. 



ACT.EONID.E. 



Eolis, Alderia, 

 Dendronotus, 

 Glaucus, &c. 



LActoeon, Placo- 

 ) hranchus.* 



The naturalists who have done most, however, to make us 

 acquainted with the beautiful constituents of this order, are 

 Messrs. Alder and Hancock. Their " Monograph of the 

 British Nudibranchiate Mollusca," in scientific and artistical 

 merit, may, without a blush, take its place beside the very 

 best works in Zoology ; and you will find the genera and 

 species illustrated therein in the most satisfactory and pleas- 

 ing manner. For the details that more immediately relate 

 to the anatomy and physiology of the animals, you must 

 resort to the essays of these authors in the annals of Natural 

 History, drawn up in part with the assistance of Dr. Emble- 

 ton. Now, Messrs. Alder and Hancock, so conversant with 

 the subject, reject, as utterly untenable, the order Phleben- 

 terata of M. de Quatrefages ; but with the Dermobranchiata 

 of the French naturalist, they propose to establish a new 

 order in the class, under the conviction that these animals 



system of M. de Quatrefages nothing more or less than an unraveled liver." 

 — Allman in Ann. and Mag. N. Hist. xvi. 156. 



* Ann. and Mag. N. Hist. xvi. 161. 



