Kingsbury, Oblongata in Fishes. 31 



terminations of a nerve fiber are important and constant, while 

 the intermediate course is due more to advantage and may vary. 

 Viewing this from the standpoint of two opposed theories of 

 nerve development and the relation of nerve fiber and ganglion 

 cell, it would be in one case the central and in the other the 

 peripheral region that is the center of growth and constant ; 

 that is, in the first case the ganglion would be fixed and the 

 course the outgrowing neurites took to reach their destination 

 would be the easiest or shortest path ; in the second case, the 

 nerve fiber, developing as a chain of cells from the ectoderm 

 would take the easiest or shortest course to the appropriate 

 brain-center. It is the latter view of nerve development that 

 Miss Piatt's researches support. Discussion of this point will be 

 avoided here ; however, it seems that in certain fishes end-buds 

 occur in the skin of the head and in the mouth, and the nerve- 

 fibers entering the brain through a root near the Vlllth nerve, 

 reach their peripheral destination (the end-buds) through num- 

 erous nerves. In Amphibia (and higher forms) the end-buds 

 are confined to the mouth and the fibers of this root are distrib- 

 uted only to pharyngeal nerves. 



Turning to the brain of Urodeles {Necturus etc.) in view of 

 the conditions in fishes (especially Arnia), it is comparatively 

 safe to homologize the whole region dorsad of the spinal Vth 

 tract with the acusticum ; this is sustained by the ental origin 

 of the Vlllth nerve and the nerves of the lateral line system. 

 The tailless Amphibia cannot be included yet. Very interest- 

 ing would be a study of the development and structure of the 

 oblongata of the Anura to determine the regions and their ho- 

 mology. It might facilitate comparison between higher and 

 lower forms which seems unsatisfactory. The entire homology 

 of the fasciculus communis system with the tractus solitarius still 



segment enter the brain by one root, by two roots, or by several, the position of 

 the nerve-root being in great measure an expression of the co-ordinate relations 

 which the central nervous system subserves. The morphological value of the 

 nerve comes from without and 'the metameric arrangement of the peripheral 

 nerves is probably not primary, but occurs in adaptation to the segmentation of 

 the structures they supply' (Froriep, 14, p. 590)." Piatt, p. 540. 



