328 THE DOCTRINE OF DESCENT. 



their interpretation. One of these is A. Giard, in his work on the 

 " EmbryogSnie des Ascidiens." (Archive de Zoologie exp^rimen- 

 tale, Paris, 1872.) The pupil of Lacaze Duthiers says : — " La chorda 

 et I'appendice caudale sont chez la larve Ascidienne des organes de 

 locomotion d'un importance assez secondaire malgre leur generalite, 

 pour qu'on les vote disparattre presque entierement dans le genre 

 Molgula, oil ils sont devenus inutiles par suite des mceurs de I'ani- 

 mal adulte ; rhomologie entre cette chorde dorsale et celle des ver- 

 tebres n'est done qu'une homologie d'adaptaiion determinee k 

 remplir I'iodentit^ des fonctions, et n'indique pas de rapports de 

 parente immediate entre les vertebres et les Ascidiens." The author 

 thus denies the consanguinity of the vertebrate animals and Ascid- 

 ians, and traces back to adaptation the resemblance approaching 

 identity occurring in the organs of the two. The inferences in these 

 few sentences appear to us utterly at fault. The circumstance that 

 in Molgula, and many other Testacea, development takes a nar- 

 rower course, makes as little alteration in the importance of the 

 facts as, for instance, the Nauplius development of the Peneus ob- 

 served by Fritz Miiller, or the Navicula of the Molluscs, is prejudiced 

 by the fact that the other Decapods have forfeited the Nauplius 

 phase, or the Landsnails the navicula phase. But it is simply in- 

 comprehensible in what the identity of functions is to consist which 

 in the Vertebrata was capable of producing the notochord, with, it 

 is particularly to be remarked, the spinal cord (which M. Giard 

 entirely forgets) ; and, in the other case, the " homologie d'adapta- 

 iion.'' We, on the contrary, see these organs performing different 

 functions, because in the one they remain of fundamental impor- 

 tance through life, and not in the other. Thus we conversely lay 

 the stress on the morphologicsd identity accompanying functional 

 difference. M. Giard adduces no facts. 



'° T. H. Huxley, Manual of the Anatomy of the Vertebrated 

 Animals. German Ed. 



" March, American Journal of Sciences and Arts, February, 



1873- 



" Eckermann, Gesprache mit Goethe. II. 152. 



" Rousseau, Emile (CEuvres, Paris, 1820, IX. 17). "Nousn'avons 

 point la mesure de cette machine immense ; nous n'en pouvons 



