312 Dr. E. Rohde on the 



inquiry. I may be permitted here to express to the Academy 

 my thanks for its kind assistance. 



In what follows I give in outline the results I obtained with 

 regard to the nervous system in the family of the Aphroditege, 

 of which I have studied, in accordance with the newest 

 methods of investigation, the genera Aphrodite^ Hermione, 

 Sthenelais, Si'gah'on, and Polynoe. I will not here enter upon 

 a discussion and criticism of the literature of the subject, but 

 will refer the reader to a larger memoir upon the same subject 

 which will very shortly appear. 



For the understanding of the colossal nerve-fibres it is 

 necessary to preface a word or two upon the so-called Leydi- 

 gian dotted substance {Punktsuhstanz) . If the brain of the 

 Polychasta be examined in thin sections, it is seen to consist 

 of very numerous fine fibrils, which are confusedly intermixed 

 and appear sometimes as lines in longitudinal sections, some- 

 times as points in transverse sections. The ventral cord has 

 essentially the same structure, only in this longitudinal fibrils 

 predominate, which, however, are crossed by oblique and 

 transverse ones. In contradistinction to the brain, transverse 

 and longitudinal sections in the ventral cord show a different 

 picture — the longitudinal sections more lines, the transverse 

 sections more dots. The nerves emitted are exactly of the 

 same structure as the ventral cord, only in them the longi- 

 tudinal course of the fibrils a])pears still more clearly, although 

 even here straight and oblique ones are not excluded. The 

 ventral cord, therefore, is not a central organ of peculiar 

 structure, but only a somewhat more strongly-developed 

 nerve which is beset wdth ganglion-cells. Even in those 

 Aphroditeaj in which the ganglion- cells do not form a uniform 

 coat of the ventral cord, but at definite distances apart consti- 

 tute so-called ganglion-nodes, as in Hermione and Aphrodite^ 

 these ganglion-nodes are only distinguished histologically 

 from the commissures lying between them and the emitted 

 nerves by the processes of the ganglion-cells which traverse 

 the central fibrils transversely. Anastomoses between the 

 individual fibrils, by which a union of the ganglion-cells 

 would be established, I have been unable to observe, any 

 more than a breaking up of the fibrils into granules. 



In this mass of fine fibrils the colossal nerve-fibres appear 

 distinctly. They are the processes of colossal ganglion-cells, 

 which occur in the brain and ventral cord in definite relative 

 positions. The genus Sthenelais is a very favourable object 

 for the study of the colossal nerve-fibres, as in it they are 

 particularly numerous and highly developed. In Sthenelais 

 there are three kinds of them, namely: — 1, traversing the 



