Johnston, The Brain of Petroinyzon. 65 



to its fitness for respiration or the presence of food, and that 

 therefore the communis fibers all have visceral or organic func- 

 tions. A fact having an important bearing on this question not 

 before noticed, is the relatively simple character — the low grade 

 of development or differentiation — of the communis center. In 

 all vertebrates the communis center is simpler in structure than 

 the cutaneous center, and this difference is already very well 

 marked in the lowest craniates. This simplicity of the center 

 is a sure indication of simplicity in the end organs. It is scarcely 

 conceivable that the communis center, with its simple structure, 

 should received fibers from such diverse structures as the lining 

 of the alimentary canal (general visceral), end-buds in the 

 mouth and. pharynx (taste), and end-buds on the outer surface 

 serving functions of cutaneous sensation (somatic sensory). If 

 the end-buds on the surface of the body are somatic sensory in 

 function it must be supposed that they give rise to reflexes of 

 some sort connected with the external relations of the animal. 

 These must be added to the considerable range of reflexes of a 

 visceral character which must be mediated by the communis 

 center and its motor connections, — reflexes concerned with the 

 movements of the alimentary canal, the respiratory and masti- 

 catory movements, and secretory activities. It must certainly 

 be expected that if this center also has a somatic sensory func- 

 tion it should show some such differentiation and complexity of 

 structure as do the centers for general cutaneous, lateral line, 

 and auditory organs. The general and special cutaneous organs 

 do not represent so wide a range of sensory impulses as would 

 be represented by the general visceral, taste bud, and external 

 end-buds with somatic sensory funtions. From these consider- 

 ations together with those presented in the previous paper 

 ('oic) the writer is fully convinced that the end buds will all 

 prove to have visceral or organic functions. The. writer also 

 awaits with the greatest interest embryological investigations 

 which shall determine whether the buds have originated in the 

 entoderm and found their way out upon the surface of the head 

 and body through the gill slits, mouth, hypophysis, or some 

 such structure as the adhesive organ of Amia. 



