642 A. A. W. HUBREOHT. 



predecessors may only be looked upon as in any way satisfactory 

 so long as they remain on a very broad and general basis, and 

 that any very special homology said to be demonstrated ought 

 for that very reason to be more especially suspected.^ 



For my part I believe that, along the lines above indicated, 

 a comparison between Vertebrate and Invertebrate nervous 

 systems will in future prove to be more fruitful, but I wish to 

 repeat that for the present we can only indicate general points 

 of coincidence between the two, and must rigorously refrain 

 from making comparisons in detail. 



On the other hand, it is suggestive once more to consider 

 what has been recorded in my ^Challenger Report' concerning 

 the nervous system of Drepanophorus Lankesteri, when 

 compared with that of certain Annelids ; and we may, I be- 

 lieve, safely come to the conclusion which was formulated by 

 me seven years ago, but which I now hold to be much more 

 solidly established, that we have in the Nemertea an important 

 group through which definite glimpses may be obtained at the 

 sources from which both Chordata and Appendiculata (Ray 

 Lankester) have respectively sprung. The proposition first 

 formulated by Gegenbaur, about the phylogenetic origin of 

 the ventral nerve-cord and oesophageal ring of the Annelida 

 out of ancestors with lateral cords, has obtained new support 

 from the arrangement which was met with in the species just 

 mentioned. "And just as we have before tentatively discussed 

 the question, in how far remnants of the lateral cords were 

 retained in those descendants in which the median one had 

 been raised to the dignity of a medulla spinalis (the Verte- 



' Bateson (loc. cit., p. 562) seems to take a similar view of the efforts here 

 alluded to. He says : " No doubt the cranial nerves may, by arbitrary 

 divisions and combinations, be shaped into an arrangement which more or less 

 simulates that which is supposed by some to have been present in the rest of 

 the body, but little is gained by this exercise beyond the production of a false 

 symmetry." — Dohrn himself, whose suggestions have so largely contributed 

 to the accumulation of all this conflicting evidence, is now rather in the 

 position of Goethe's Zauberlehrling, and writes (' Studieii,' x, p. 468,1885): 

 " Auch auf diesem Gebiet (die Frage nach der Bedeutung der Hirnnerven) 

 bildet die bisherige vergleicheude Anatomie das Bild eines auf stiirmisclier 

 See steuerlob herumgeschleuderten Schiffes." 



