312 



thesis which he here tries by a long and laborious argument to estab- 

 lish. The nerve centers furnish as good a clue to the mere fact of 

 relationship or homology between two nerve components as does the 

 peripheral distribution. Indeed, in basing his argument upon the ho- 

 mology of the "Lobus trigemini", Allis recognizes the importance of 

 the central relations, but he has not studied them with anything like 

 the care that has characterized his numerous researches upon the peri- 

 pheral system. The centers for each of the nerve components are 

 constant in the vertebrate series and are sharply distinguished both 

 by their histological structure and their secondary connections. So 

 separate and so stable are the respective centers for the lateral line 

 and end bud fibres that it is utterly impossible for fibres or centers 

 to "undergo modification" of any sort such as I understand Allis to 

 mean in what he says at the top of p. 225. This modification seems 

 to imply a change of center of the fibres of the ophthalmicus super- 

 ficialis from the lobus vagi to the so-called lobus trigemini, in Aci-^ 

 penser. Such a change of center would imply necessarily a change 

 of function of the end organ determined by the secondary connections 

 of the centers. In this case the sense organ must change from an 

 organ with visceral function (e. g. taste) to an organ with a somatic 

 function (e. g. touch or pressure in relation to equilibration). We have 

 no evidence that any such change of function ever takes place. On 

 the contrary, we find frequently reduction of one set of sense organs 

 and increase of another set, together with corresponding changes in 

 the brain centers, brought about by changed conditions of life and 

 having relation to the needs of the organism. In contrast to this 

 doctrine of modification I would emphasize the constancy of the chief 

 divisions of the nervous system, and the inseparable and unchangeable 

 unity of the central and peripheral elements of each functional division. 



Paper scited. 



1) Allis, The Cranial Muscles and Cranial and First Spinal Nerves 

 in Amia Calva. Journ. Morph., Vol. 12, 1897. 



2) — , The Lateral Sensory Canals, the Eye-Muscles, and the peripheral 

 Distribution of certain of the Cranial Nerves of Mustelus laevis. 

 Q. J. M. S., Vol. 45, November 1901. 



3) GoRONOwiTSCH, Das Gehirn und die Cranialnerven von Acipenser 

 ruthenus. Morphol. Jahrb., Bd. 13, 1888. 



4) Johnston, Hind Brain and Cranial Nerves of Acipenser. Anat. 

 Anz., Bd. 14, 1898. 



5) — , The Brain of Acipenser. A Contribution etc. Zool. Jahrb., Abt. 

 f. Anat. u. Ontog., Bd. 15, 1901. 



