of the Central Nervous System in Ascidia &c. 213 



Here I shall only report what I think I have observed with 

 regard to the minute structure of the brain of the Ascidia ; 

 with respect to the more topographical description I will refer 

 to the memoirs by Co Julin and E. van Beneden, already 

 cited. 



1. I find the fibrillar central mass to consist of two consti- 

 tuents, just as already described in the Myzostomes {I. c. 

 p. 33). In the first place, a fibrillar loeb. This web 

 is diffused throughout the whole mass, and gives it, in 

 section, that spongy appearance which led Leydig to imagine 

 that the fibrillar mass, or, as he called it, the " Punktsub- 

 stanz," has a spongy structure. It consists, however, in my 

 opinion, of fine fibrillar, which are most intimately intermixed, 

 so that they appear to be interwoven with each other, but, at 

 any rate, in general, without anastomosing with each other in 

 the manner recently described in the case of the Rhipidoglossa 

 by Dr. Bela Haller ■^. It is in the settlement of these difficult 

 points in the lower animals that we are specially brought to 

 feel how far our modes of investigation are still from being 

 sufficient. I have certainly seen nearly the same images that 

 Dr. Haller describes, and when his drawings are compared with 

 mine this will certainly be the impression ; but I am afraid 

 that what Dr. Haller describes and figures as a fibrillar, 

 anastomosing network is in reality nothing of the kind, but is 

 connective substance, or, as Leydig calls it, " spongio- 

 plasma," which, in my opinion f, encloses and isolates the 

 individual fibrilla?, and does not, as Leydig thinks, extend as 

 a spongy tissue throughout the whole mass. If we compare 

 sections of the fibrillar central substance with transverse sec- 

 tions of peripheral nerves it must certainly be confessed that 

 in appearance these resemble each other ; in both we shall see 

 a distinct reticular web, consisting apparently of anastomos- 

 ing fibrilla3 ; the only difference is that in the divided nerve 

 the meshes are considerably coarser. We know, however, 

 that here an isolation really occurs^ and that every mesh is in 

 reality a divided tube of spongioplasma, which encloses a hya- 

 loplasmatic cord, a " nerve-cylinder," which in its turn either 

 originates from or at any rate (with but few exceptions) 

 traverses the fibrillar central substance. If it is connected 

 with that substance, I cannot see but that to a considerable 

 extent it testifies in favour of the view that the reticular web 

 which one sees by the ordinary methods of preparation is in 

 reality connective substance or " sponyioplasmaf'^ which sur- 



* For his work see furtlier on, p. 224. 



t Just as I liave already stated in the description of the nervous system 

 of tlie Myzostomes (/. c). 



