GANGLIOX-CELLS. 



139 



Fig. 96. 



coils, and Beale thinks the coils are more numerous in older cells — for 

 in some cases the smaller fibre (answering to the spiral one elsewhere) 

 is not coiled ; the cells in such cases he considers to be young or 

 recently formed. 



Beale's observations were chiefly made on the ganglia of frogs, the cells of 

 which have very commonly a pyriform shape like the one represented in the 

 figTire. In mammalia they are more spheroidal, and the obsei-vation of their 

 connection with fibres is more difficult ; but from examinations in mammalia, he 

 was led to infer that the relation of the cells and fibres is essentially the same as 

 in frogs. . 



Two subsequent ■m.iters, Julius Arnold, and L. G. Coui-\-oisier. confirmed the 

 original obsei-vation of Beale in almost every point ; but whilst the last-named 

 observer described the two fibres as connected with the substance of the cell and 

 at its surface onlj' — or, at least, could not obtain satisfactory evidence of theii- 

 passing- into the interior — Ai'nold. and (after him) Courvoisier describe (as had 

 previously been done by Harless and others) the straight fibre as traceable into the 

 nucleus, with which Arnold thinks its medullary sheath, here altogether inconsider- 

 able, is continuous, whilst the axial part ends in the nucleolus, which he regards as 

 the knobbed end of the axis-cylinder (fig. 95). They both describe a network of ex- 

 quisitely fine fibrils, which, springing from tlu nucleolus as a centre, traverses the 

 suljstance of the cell and comes to the surface between the cell-body and its sheath, 

 and finally unites into the siiii-al fibre. According to this account, the nucleolus 

 is, as it were, the end of the straight fibre 

 and beginning of the spiral one, or rice 

 vcDid ; or, at least the point of organic 

 connection between them in the cell. 

 Courvoisier describes both fibres as ac- 

 qvuring a medullary sheath, the straight 

 one first. He has found the above de- 

 scribed structure in the ganglia of fish, 

 birds, and mammals ; but -v^hilst in the 

 frog the cell has never, or scarcely ever, 

 more than one straight and very rarely 

 more than one spiral fibre, he finds that in 

 other vertebrates a cell may give off such 

 twin fibres from two or more par-ts of its 

 circumference. 



With regard to the alleged connection 

 of the fibres with the nucleus and nu- 

 cleolus of the cell, we would remark 

 that no such connection is obseiwable in 

 other nerve-cells. — those of the spinal 

 cord for instance. And recent obseiwers 

 have for the most part failed to cor- 

 roborate the statements of Arnold and 

 Courvoisier. On the other hand, it is 

 probable that the primitive fibrils of the 

 neiwes are continuous with one another 

 through the body of the cell. 



Besides such cells as have now been 

 described, others are not unfrequently 

 met with in which there is a different 

 aiTangement. In the spinal ganglia of 

 the skate, torpedo, dogfish, &c., as first 

 pointed out by E. AVagner, two fibres 

 are connected with each ganglion-cell at 

 opposite sides — one directed centrally to- 

 wards the root of the nerve, and the other 

 outwardly towards its branches (fig. 'JG). 



Fig. 96. — Bipolar Ganglion-Cell frok 

 Spinal Ganglion of Pike. 350 Diame- 

 ters. ^^Kolliker.) 



a, Capsule of cell contiiuions with, h, 

 sheath of nerve, c, medullary sheath. 

 d, axis-cylinder, e, body of cell. 



