INTRODUCTION. Xxix 



" We may trace," says Professor Owen,* '' in the heart 

 of the Crustacea, a gradational series of forms, from the 

 elongated, median, dorsal vessel, to the short, broad and 

 compact muscular ventricle in the lobster and the crab. 

 In all the Crustacea, as in all the other articulate animals, 

 the heart is situated immediately beneath the skin of the 

 back, above the intestinal tube, and is retained in situ by 

 lateral pyramidal muscles. In the lower, elongated, many- 

 jointed species of the Edriophthalmous Crustacea the heart 

 presents its vasiform character: it is broadest and most 

 compact in the crab. In this series we may trace a 

 general correspondence in the progressive development 

 of the vascular as of the nervous system, concomitant 

 with the concentration of the external segments, and 

 the progressive compactness in the fomi of the entire 

 body." 



Corresponding with the view which has been taken of 

 the gradual condensation of the segments of the body 

 and the centralization of the viscera, is that of the nervous 

 system as seen in the various forms of Crustacea as they 

 rise in the scale of organization. An elaborate detailed 

 description of all the gradations formed the substance of 

 an admirable essay f by the distinguished naturalists so 

 often quoted, of whose labours an excellent abstract is 

 given by my friend Professor Rymer Jones, in his " Ani- 

 mal Kingdom." | 



In Talitrus, where the insectiform arrangement is the 

 most obvious, and where every pair of ganglia consists of 



* L. c. p. 180. 



t Messrs. Audouin et Milne Edwards, " Recherches Anatomiques sur le 

 Systeme Nerveux des Crustaces." Ann. des Sc. Nat. t. xiv. 

 J L. c. p. 337. 



