REPORT ON THE NEMERTEA. 145 



All these considerations have induced me to give this rapid outline sketch of the 

 degree of comparison which I hold to exist between Chordate and Nemertean (more 

 especially Palajonemertean and Schizonemertean) nervous systems, although I am per- 

 fectly aware that there is a growing tendency among those authors at present occupied 

 with cjuestions concerning the morphology of the Vertebrate nervous system (Froriep, 

 Baldwin Spencer, Beard, Cunningham, Kleinenberg, and many others) to accept 

 Semper 's and Dohrn's views of the Annelidan descent of Vertebrates. Wiedersheim, 

 in the new edition of his " Vergleichende Anatomie " (1886), does not even hesitate to 

 bring these results in their unripe phase before the more extensive public of students, and 

 this generally in acquiescent terms. It is curioiis to see how, e.g., the question of the 

 cephalic nerves and their comparison to spinal nerves, that of the nerve-roots, the 

 cephalic ganglia and their respective connecting trunks, have given occasion to the most 

 diverse twisting and retwisting of the facts in order to bring out a fixed scheme or 

 diagram, which might then be compared to what obtained in Annelids, and in which 

 the highest degree of similarity between the respective somites might be obtained, thus 

 establishing a preconceived idea of the Vertebrate ancestor as a most rigorously seg- 

 mented animal. The value of these speculations has been already tested above, and I may 

 be allowed once more to express my conviction that our comparisons between the Chordata 

 and their lower Invertebrate predecessors may only be looked upon as in any way satis- 

 factory 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 

 above (p. 89) concerning the nervous system of Drepanophorus Icmkesteri, when 

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



1 Bateson {loc. cit., p. 562) seema to take a similar view of the efforts here alkided 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 

 (Studien, X., p. 468, 1885)—" Auch auf diesem Gebiet (die Frage nach der Bedeutung der Hirnnerven)bildet die bisherige 

 vergleichende Anatomie das Bild eines auf stiirmischer See steuerlos herumgeschleuderten Sohiffes." 



(ZOOL. CHALL. EXP. — PART LIV. — 1887.) °-"^ ^^ 



