igo STRONG. [Vol. X. 



example, Goronowitsch, namely, the nuclei of the motor roots. 

 This, of course, does not affect the actual similarities existing. 

 When we compare this description with the condition in the 

 Amphibia we find them, I think, similar. Excluding the motor 

 nuclei, we have in both cases the bundles of fine fibres, the 

 ground substance, and nerve cells, arranged in practically the 

 same manner. The fasciculus communis itself represents 

 the outer layer described by Mayser, the peculiar ground-sub- 

 stance the second layer, and the nerve cells found by Mayser 

 are represented in the tadpole by the group of ganghon cells 

 accompanying the fasciculus; in Cryptobranchus partly, at 

 least, by Osborn's " nucleus of small sensory cells by which 

 the fasciculus communis is apparently reenforced" (45); and 

 in the higher forms by the "sensory nucleus" of the IX + X, 

 and probably by other cells in the vicinity of the fasciculus 

 solitarius. 



One great difference is apparent between this tract, or tracts, 

 in fishes, on the one hand, and in Amphibia — especially Anura, 

 — together with the higher vertebrates, on the other, namely, 

 that in the fishes it is much more developed. This is easily 

 intelligible when it is considered that it is essentially the 

 central organ of the branchial nerve supply. Its great develop- 

 ment in fishes is correlated with the development of the gills, 

 and where these are in process of reduction or lost it is 

 correspondingly reduced. 



The fine-fibred branches of the postauditory portion of this 

 component (see Table, p. 180) correspond, of course, with the 

 similar branches constituting the fine-fibred, visceral portion of 

 the IX + X in fishes, as distinguished by Stannius, Shore, and 

 others. This excludes the larger-fibred branchio-motor portion. 

 The regular arrangement of the roots, ganglia, and branches, as 

 seen in many fishes, is, in the tadpole, mostly obscured, owing 

 to causes noted above (p. 135). This arrangement is partly pre- 

 served, however, in the series of roots from the fasciculus com- 

 munis. The ganglion of the IX (ganglion C) is still separate, 

 but the ganglia of the Rr. branchiales are fused with each other 

 and also, partly, with that of the R. visceralis. Owing not only 

 to the forward position of the gills relative to the auditory cap- 



