902 



between the three types. This can be best shewn by figures, and I 

 intend shortly to publish an illustrated account. In the usual deve- 

 lopment as seen in Elasmobranchs, the ganglionic Anlagen are the 

 culprits which have hidden the true process. 



Now I don't know where the ganglionic Anlagen are in Amphioxus^) 

 — perhaps Prof. Hatschek or some other observer will investigate 

 that point — but I can in all cases leave them out of account here, 

 when I describe the formation of the central nervous system of Verte- 

 brates as the sinking of an open plate below the epiblast and the 

 growth of the ordinary epiblast over the open sunken plate. — In 

 reality it is more complicated, but that is what it really comes to. 



True the plate tends to close and form a tube before the epiblast 

 has closed over it, that makes no diflerence; for it does not form a 

 tube for a long time after its separation from the outer layer, and the 

 latter really unites over an open plate just as in Amphioxus. In deal- 

 ing with Teleosteans one must leave the transitory „Deckschicht" out 

 of account. Dr. Ziegler assures me, and I agree with him, that it 

 has no morphological importance. Then at its basis, the process in 

 Teleostei is the sinking below the epiblast of a plate the two halves 

 of which are closely folded together. — Over this folded plate the or- 

 dinary epiblast meets and fuses. (See Goronowitsch's paper, Mor- 

 phol. Jahrb. Bd. 10, p. 376, the figures do not show this very clearly.) 

 Another point, the neural plate has no outer layer of ordinary epiblast, 

 but is composed of two bands of neuroepithelium separated in the 

 middle by what soon becomes a ciliated groove. In other 

 words, the neural plate in all Vertebrates, above Am- 

 phioxus^), is a paired structure the two halves being 

 separated in the median line by a ciliated groove, just 

 as in developing Annelids. Probably like the groove of Anne- 

 lids it is composed originally of two rows of cells, at least in Triton 

 and Salamandra I have noticed that the ciliated groove arises from 

 two cells in the middle line. This ciliated groove may be seen in 

 embryos of nearly all Vertebrates immediately after the meeting of 



1) I strongly suspect that they are included in the medullary plate 

 of this „primitive" animal. One thing may be have noted viz — that 

 certain of Hatschek's figures of later stages do not agree with those of 

 KowALEvsKT, and Hatschek makes no indication of the difference. 



2) Amphioxus is hardly likely to form an exception in this respect. 

 Unfortunately Hatschek's figures of Amphioxus larvae are very diagram- 

 matic, and his statement that the central canal is lined throughout by 

 cilia in young larvae is probably not correct. He has not figured the cilia. 



