216 Mr. F. Nansen on the Histological Structure 



remain for the present somewhat doubtful as to their actual 

 presence. 



If I now summarize my results with regard to the nerve- 

 cells and their processes in the brain of the Ascidia, they 

 prove to be in the fullest agreement with the results at which 

 I arrived in the Myzostomes, and in their principal features 

 also with results obtained by Dr. Bdla Haller in the Rhipi- 

 doglossa, only I must point out that in the Ascidia I have 

 not succeeded in demonstrating undoubted anastomoses be- 

 tween the processes of the ditiferent cells, such as Haller 

 describes in the E-hipidoglossa. 



3. As regards the origin of the nerve-cylinders, as my 

 investigations hitherto have not been specially directed to this 

 point, only this much can be said about it, that from what I 

 have hitherto seen there appears here also to be an agreement 

 with my earlier results in the Myzostomes. There would 

 consequently exist two forms, one originating directly from 

 nerve-cells, and one originating from the tibrillar web — 

 therefore two forms just such as Golgi has demonstrated in 

 man. 



4. With respect to the fourth point, it is not difficult to 

 observe nerve-cells situated near the origin of the peripheral 

 nerves and emitting their processes directly into the peripheral 

 nerves without first passing through the fibrillar central mass. 

 I have also found, in the peripheral nerves even at a distance 

 from the brain, nerve-cells which sent their nervous pro- 

 cesses in a peripheral direction and not inwards towards the 

 central organ. This is therefore a condition which stands in 

 the most perfect agreement with the condition in the Myzo- 

 stomes, and does not agree with Vignal's * (and Ranvier's) 

 assumption of the non-existence of such cells in the voluntary 

 nervous system. Whether side-branches are not given off 

 from the nervous prolongations of these cells, by which they 

 are connected with the central fibrillar web, I have not yet 

 been able to ascertain, although it certainly appears to me to 

 be probable. 



As regards the sixth and seventh points, I will reserve my 

 reference to them until later on, when it will be possible to 

 go into the matter more in detail ; for, in the first place, the 

 investigations in this direction are still far from complete, and, 

 secondly, a hasty description of them would lead only too 

 easily to misconceptions. 



Summing up the main points in the above superficial de- 

 scription of the Ascidian brain and comparing it with my 



* Vignal, " Rech. histol. sur les centres ncrveux de quelques inverte- 

 brt?s," in Arch, de Zool. Exp^r. s(?r. 2, tome i. (1883). 



