History of a transient nervous apparatus in certain Ichthyopsida. 399 



some zoologists would immediately have recourse to Amphioxus as 

 the form in which the key to the problem was to be sought, and 

 already indications of such an intention are not lacking. In a letter 

 from Prof, von Kupffer, quoted by Kölliker in the new edition ^) 

 of the "Gewebelehre", among other statements in reference to the 

 transient ganglion-cells, this passage occurs : — "es sind höchst wahr- 

 scheinlich ancestrale Elemente, die auf Amphioxus zurückleiten" ^). 



1) No. 8, p. 172. 



2) In VON Kupffer's recent memoir, cited on page 330, the Munich 

 anatomist has recorded some observations on these cells in Petromyzon 

 embryos. According to Feoriep (in: Ergebnisse der Anat. und Ent- 

 wicklungsgesch., V. 3, p. 450) von Kupffer looks upon the transient 

 nerve-fibres as the homologues of the dorsal spinal nerves of Amphioxus. 

 It is not easy to understand why a supposed reduction in the branchial 

 system, of whose former existence posterior to the pronephros there 

 exists no evidence , should cause these nerves to become transitory. 

 The whole hypothesis requires so many subordinate suppositions and 

 depends so absolutely on a postulated genetic relationship of Amphioxus 

 to the fishes, that its weakness is self-evident. Does Amphioxus ever 

 present at any stage of its development evidence of a system of transient 

 ganglion-cells and nerves ? I have long suspected that investigation may 

 ultimately give an affirmative answer to this question, at any rate, we 

 are not at present in a position to deny the possibility of such being 

 the case. Do the dorsal spinal nerves take their origin from large 

 superficially - placed ganglion-cells ? Erom a drawing by Rohde, figured 

 in Willey's 'Amphioxus' (fig. 46, p. 91) the answer to this query 

 appears to be in the negative. Has Amphioxus an aggregation of 

 hundreds of ganglion-cells on its spinal cord? Again the reply is no. 

 Lastly, it may be asked , can von Kupffer bring all the undoubted 

 facts of this paper into harmony with views, which, as I understand 

 them, appear to rest solety on a framework of hypotheses? 



Since the above was written, von Kupffer's memoir (Studien zur 

 vergleichenden Entwicklungsgeschichte des Kopfes der Kranioten, Hft. 2, 

 1894) has reached my hands. After reading it, there seems to me to 

 be no occasion for altering anything of the preceding criticism. In 

 consequence of remarks that have been made to me by German col- 

 leagues I feel bound to state that in what relates to the transient 

 system (so-called "Rohon's cells" of von Kupffer) the Munich ana- 

 tomist has confirmed previous statements of my own, und in no respect 

 has he recorded facts concerning it which had not previously been 

 described by me. von Kupffer would appear to be unacquainted with 

 the paper published in the Proceedings of the Royal Society, London 

 1889, otherwise he would have noted that the occurrence of these transient 

 cells as there noted for Petromyzon, Amphibia and Ganoidei 

 {Lepidosteus). 



