of the Central Nervous System in Ascidia c&c. 217 



former description of the nervous system of the Myzostomes, 

 it will be seen that we have here obtained a good confirmation 

 of the results furnished by the latter. It may now be of 

 interest to investigate how the conditions stand in the lowest 

 forms of Vertebrata. Of these I have as yet properly inves- 

 tigated only the hag {Myxine glaiinosa). 



The Central Nervous System in the Hag (Myxine glutinosa). 



Of this interesting animal it is easy, at Alverstrommen, to 

 obtain abundant material ; but the tims was too short to allow 

 any thorough investigation to be undertaken; during the coming 

 summer I hope to have an opportunity of doing this, and 

 it may even be expected that with new fresh material I may 

 try new and better modes of investigation. Here therefore 

 I will only express myself with extreme brevity. 



So far as I know, no one has recently paid particular atten- 

 tion to the histological structure of the central nervous system 

 of Myxine ; on the other hand, something is known of the 

 histology of the nervous system in the genus Petromyzon. 

 In Dr. Ahlborn^s memoir, " Untersachungen tlber das Gehirn 

 der Petromyzonten " *, there is a detailed description of the 

 topography of the brain in Petromyzon, as also a portion of 

 the histology of the brain and spinal cord ; there will likewise 

 be found in it a list of the earlier literature of the subject. 

 Our histological knowledge of Petromyzon also is unfortu- 

 nately rather defective, and there still remains much to be made 

 out. 



It appears that the structure of the nervous system in 

 Myxine and Petromyzon^ notwithstanding many differences, is 

 on the whole tolerably accordant. It is especially to the spinal 

 cord that I have hitherto directed my attention. 



As is known, the spinal cord in Myxine, as in Petromyzon, 

 has that flat band-like form which at once catches the eye in 

 transverse sections. On the ventral surface there is a con- 

 siderable longitudinal depression or groove, a kind of sulcus 

 longitadinalis ventralis, if one may call it so ; on the dorsal 

 surface, on the contrary, there is no trace indicative of such a 

 groove. 



The space between the central canal and the ventral longi- 

 tudinal furrow is occupied by a considerable markedly fibrillar 

 mass of connective tissue, in which the fibrill^e from the two 

 sides cross one another, and, at any rate for the greater part, 

 are in connexion with the pia mater on both sides of the 

 longitudinal furrow ; a similar mass has also been described 



* Zeitschr. fiir wiss. Zool. Bd. xxxix. (1883), pp. 191-294. 

 Ann. do Mag. N. Hist. Ser. 5. Vol. xviii. 15 



