106 ADAM SEDGWIOK. 



region of the fore-gut ends at the level of the fifth anterior 

 root, and the first posterior root and the first sympathetic 

 ganglion occur at the level of the sixth anterior root. In 

 older embryos, in which the branchial region extends much 

 further back and overlaps a number of fully-formed spinal 

 nerves, the original sympathetic ganglia which were formed in 

 connection with the ganglia of these spinal nerves thus over- 

 lapped are found to have disappeared. The first sympa- 

 thetic ganglion appears always to be just behind 

 the branchial region, as in the adult, and sympa- 

 thetic ganglia are formed in Scyllium in connec- 

 tion with nerves which are without a posterior root. 



Gaskell reproaches v. Wijhe with not knowing the true 

 meaning of a sympathetic ganglion, and one is tempted to ask, 

 does Gaskell himself know much more about it, or throw any 

 light upon the question ? He says ('Journal of Physiology,' 

 vol. X, p. 162) that a sympathetic ganglion is the ganglion of 

 the anterior root of a spinal nerve which has travelled to a 

 variable distance from the central nervous system. As Dohrn 

 (seventeenth study, 'Naples Mit.,' Bd. x) very properly in- 

 sists, this view is at variance with the known developmental 

 history of the ganglion — which I am able to confirm so far as 

 its nuclei are concerned, and with the reservations necessitated 

 by the views set forth in this paper — and I am now able to 

 state that it is at variance with the fact that sympathetic 

 ganglia are entirely absent from those spinal nerves in which 

 the posterior root fails to reach its full development. In fact 

 one may say of these ganglia that they are always absent when 

 the posterior roots are not developed. 



With regard to the fate of the neural crest described in this 

 paper, I should mention that I strongly hinted that it gave rise 

 to nuclei which entered the reticulum in my ' Notes on Elas- 

 mobranch Development,' p. 581, published in 1893; and that 

 Goronowitsch arrived independently at the conclusion that it 

 broke up into mesenchyme in the bird, and published his 

 results at some length in 1893 (' Morph. Jahrbuch,' Bd. xx) ; 

 but Goronowitsch failed to recognise the reticulum, and he was 



