LAMARCK'S THEORY OF DESCENT 



291 



degraded organization, and are nearer the fishes" 

 (P- 155)- 



Referring on the next page to the fishes, he re- 

 marks : — 



" Without doubt their general form, their lack of 

 a constriction between the head and the body to 

 form a neck, and the different fins which support 

 them in place of legs, are the results of the influence 

 of the dense medium which they inhabit, and not 

 that of the degradation of their organization. But 

 this modification {degradation) is not less real and 

 very great, as we can convince ourselves by examin- 

 ing their internal organs ; it is such as to compel us 

 to assign to the fishes a rank lower than that of the 

 reptiles." 



He then states that the series from the lamprey 

 and fishes to the mammals is not a regularly gradated 

 one, and accounts for this " because the work of 

 nature has been often changed, hindered, and di- 

 verted in direction by the influences which singu- 

 larly different, even contrasted, circumstances have 

 exercised on the animals which are there found ex- 

 posed in the course of a long series of their renewed 

 generations." 



Lamarck thus accounts for the production of the 

 radial symmetry of the medusae and echinoderms, 

 his Radiaires. At the present day this symmetry is 

 attributed perhaps more correctly to their more or less 

 fixed mode of life. 



" It is without doubt by the result of this means 

 which nature employs, at first with a feeble energy 

 with polyps, and then with greater developments in 

 the Radiata, that the radial form has been acquired ; 



