MILNE-EDWARDS. 593 



stellar constellations that crowd the glorious vault of heaven. 

 — Guided by these views, Milne-Edwards classifies the Gas- 

 teropods thus: — 



Class— GASTEROPODA. 



Cephalous Mollusca, with a fleshy foot for locomotion, 

 formed by a posterior lobe of the head ; the organs of gene- 

 ration unpaired and unsymmetrical, and the entire organ- 

 ism modelled on a spiral line, either in the larva state only 

 or throughout life. 



Typical Group, or Subclass I. NORMAL GASTERO- 

 PODS. 



Foot fleshy, flattened, and very large ; abdomen well de- 

 veloped, &c. 



1 Section. Pulmonated Gasteropods. 



Larva with a naked head, &c. ; vessels of the lesser circu- 

 lation reticulated ; androgynous. 



2 Section. Branchiferous Gasteropods. 



Larva with cephalic swimmers, &c. ; vessels of the lesser 

 circulation fasciculated. 



Order I. Opistobranchia. Cervical region naked, &c. 

 Order II. Prosobranchia. Cervical region surmounted 

 with a vaulted pallial cavity, &c. 



Aberrant Group, or Sub-class //.—SWIMMING GAS- 

 TEROPODS, OR HETEROPODS. 



Foot fleshy, vertical ; abdomen rudimentary, &c. 



Satellitious group of Gasteropods pendulous from the 



Prosobranchia. 



Family, CHITONID^E. Cephalous Mollusca ? with a 

 fleshy foot ; the body subannular; generative organs paired 

 and symmetrical : a medial dorsal vessel, &c* 



These great reforms of Milne-Edwards derive support 

 from the delicate and elaborate dissections of his young 

 friend, M. Emile Blanchard. This adroit and gifted natu- 

 ralist, in addition to the characters above assigned to the Opis- 

 tobranches, tells us that the cephalic ganglia of the nervous 

 system have a closer centralisation than they have in other 

 Gasteropods, — a fact which had been previously made known 

 to us, in many Nudibranches, by Mr. Hancock and Dr.Emble- 



* Annates des Sciences Naturelles, ix. (1848), p. 102 — 112. It appears 

 the classification was first published in August, 1846. — Mr. J. E. Gray lias 

 defined the genera of Chitonidn? in the Ann. and Mag. N. Hist. xx. 66. 



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