328 JOHN BEARD, 



gemacht, und speciell die Bildung und Beziehungen der sog. riesigen 

 Ganglienzellen der Selachier und von Lophius piscatorius untersucht. 

 Aber die Fortsetzung dieser Studien hat mir so unerwartete Zustände 

 der Ontogenese des Medullarrohres, wenigstens bei Selachiern und 

 Teleostiern, offenbart, dass ich es vorziehe, die Erscheinungen der 

 Ontogenese des Centralnervensystems im Zusammenhange in einer 

 oder mehreren separaten Studien zu erörtern etc." 



Ever since my migration to Edinburgh in 1889 the problems of 

 these transient ganglion-cells had exerted an increased fascination over 

 me — a fascination still more intensified by the discovery that in 

 Raja hatis an lObject had been found easily obtainable, and withal 

 one promising much interesting information concerning the transient 

 system. 



Dohrn's memoir on its arrival found me immersed, in the inter- 

 vals of exacting duties, in an investigation of a large series of Raja 

 embryos. To escape the total loss of priority of my results as they 

 then appeared to stand, by a prior publication on Dohrn's part, a 

 preliminary paper was written and published in the Anat. Anz. 1892^). 



The summary of my results at that date is taken verbatim 2) 

 from p. 203 — 205 of the preliminary paper ^). 



"Except as above noticed, or hereinafter mentioned, the account 

 given in my Lepidosteus note (1889) may still stand pro tan to. 



The apparatus of ganglion-cells does not appear to extend quite 

 to the extreme portion of the spinal cord. In Raja it certainly be- 

 gins at about the 6"' trunk-somite (include the hypoglossus segments), 

 reaches a maximum in the region of the 11 ^^, maintains this with 

 slight segmental variations until the 25tii or 26th somite is reached, 

 i. e. over some 15 segments, and in early stages terminates about the 

 31st trunk segment. Absent or undeveloped in early stages posterior 

 to this region, it is found in older embryos extending along the whole 

 length of the tail. 



Its nerves may be either simple (spun) axis-cylinders, or compound 

 non-medullated ones, possessing a neurilemma, and formed by chains 

 of nerve-forming nuclei or cells. Cases of "contact" between nerve 



1) No. 3. 



2) In this summary a number of errors have been eliminated and 

 only those portions have been retained of whose accuracy renewed ob- 

 servations have convinced me. 



3) No. 3. 



