4 ^Jouryial of Comparative Neurology and Psychology. 



are probably used in conjunction in locating food. These experi- 

 ments, reinforced by the complete isolation of the gustatory fibers 

 and gustatory centers microscopically, leave no doubt that we 

 have here a sensory system quite distinct functionally and struc- 

 turally from any other cutaneous sense organs. 



As to the exact time and place of appearance and the direction 

 of spreading of the buds, less work seems to have been done. 



Allis ('89) calls attention in Amia to the time of appearance 

 of what he takes to be terminal buds and describes briefly the 

 manner of spreading posteriorally from the anterior parts of the 

 head back to the body. He describes (p. 509) and figures the 

 terminal buds as appearing as whitish lines, usually parallel with 

 the lateral lines of the head, that later break up into individual 

 buds. The serial arrangement disappears as the buds become 

 more numerous. 



Johnston ('05a) states that buds are present in the branchial 

 region only of' the Ammocoetes stage of Petromyzon but that they 

 are present in the skin also of the adult. Corregonus and Cato- 

 stomus sp. were studied also in serial sections, and the taste buds 

 of the pharynx found to be much more numerous and highly de- 

 veloped than elsewhere. Buds were found in the oesophagus and 

 on the roof and floor of the mouth but in both places were smaller 

 than those in the pharynx. No buds were found on the skin of 

 the body except in a specimen taken some days after hatching. 

 These facts, /. e., the earlier appearance of the pharyngeal buds, 

 their larger size, and the fact that all taste buds are innervated 

 by communis fibers, inclined Johnston to the opinion that buds 

 have spread from the endoderm to the ectoderm. 



(b) The Communis System. — The need of the application of 

 histological methods in the study of peripheral nerves and the 

 substitution of components as physiological and morphological 

 units instead of nerves may be traced to Gaskell ('86, '89). The 

 two-root theory of Bell had dominated the study of spinal and 

 cranial nerves from the time Bell's law was enunciated in 1810 

 until Gaskell proposed what is called the four-root theory. Ac- 

 cording to Gaskell a typical spinal nerve contains four roots, 

 somatic sensory, somatic motor, splanchnic sensory and splanchnic 

 motor. 



Strong ('95), following a suggestion of H. F. Osborn ('88) 

 that it might be possible to analyze the cranial nerves on the basis 



