224 Mr. F. Nansen on the Histological Structure 



description previously given of the ventral covdi o{ Myzosto^na, 

 fin agreement to whicli I certainly will not ascribe great 

 importance, but which has nevertheless struck me as remark- 

 able and as, at any rate to a certain extent, indicative of a 

 homology between the spinal cord and the ventral cord. As 

 w^e have seen above, the nerve-fibres traversing the spinal cord 

 longitudinally are essentially situated towards the ventral 

 •surface, while the fibrillar web appears especially on the 

 dorsal side. In the ventral cord of Myzostoma^ on the con- 

 trary, the fibrillffi which run longitudinally were situated on 

 the dorsal side, while the mass of the fibrillar web constituted 

 the ventral part of the ventral cord. Here also, especially, 

 were situated the cells, the nervous processes of which divide 

 up into the fibrillar web; while the cells which send their 

 processes directly into the peripheral nerves belong essentially 

 to ihe dorsal surface, therefore altogether exactly the opposite 

 of what we found in Myxine. However, if we regard the 

 ventral cord and the spinal cord as homologous, we must also 

 imagine the ventral cord as turned with its dorsal surface 

 downwards, that is to say the dorsal surface in Myzostoma 

 corresponds to the ventral surface in Myxine^ and vice versd ; 

 and if Ave consider the above-mentioned conditions we shall 

 find the most beautiful agreements. According to Dr. Haller's 

 description it appears tliat in this respect a similar condition 

 to that here mentioned in the Myzostomes occurs in the K.hi- 

 pidoglossa. As already said, I will not from our present stand- 

 point ascribe any greater significance to this ; but it never- 

 theless seems to me to be possible that, when more thoroughly 

 investigated, it may show itself to have a deeper foundation. 



After these investigations were undertaken last summer at 

 Alverstrommen, and at the same time that my memoir on the 

 structure of the Myzostomes was printed in the winter, the 

 very remarkable memoir by Dr. Bela Haller on the structure 

 of the central nervous system in the Ehipidoglossa * ap- 

 peared in the ' Morphologisches Jahrbuch,' in which that 

 author has arrived at results which in many respects stand in 

 striking agreement with those above detailed and with the 

 results obtained in the case of the Mj-zostomes. This is 

 certainly not the place to go in detail into this memoir ; but 

 I will state in a few words the points in which, from my 

 investigations, I cannot perfectly agree with Dr. Haller. 



He has, like myself, two forms of peripheral nerve-fibrillje, 

 some which originate directly from ganglion-cells and others 



* " Untersuchungen liber marine Illiijiidoglossen," in Morpliol. JaLrb. 

 Bd. ii. 1886, pp. 321-436. 



