104 'Journal of Comparative Neurology and Psychology. 



represents the simplest kllo^v^l pliysiological unit of the somatic 

 nenro-miiscular system, or of the somatic "action system." The 

 relation of this unit to any of the more complex neuro-muscular 

 processes is certainly an essential factor in the problem of behavior, 

 or of physiology in the broadest sense. 



In presenting the mode of locomotion of the amphibian embryo 

 it is not my intention to antagonize the current explanation of the 

 propelling factors of the swimming movement of fishes, ordinarily 

 described as being, in effect, the same as that of a sculling oar. The 

 latter explanation, so far as I am aware, is offered with reference to 

 the adult fish, and it might not apply to an embryonic or very young 

 fish. Quite conceivably, the swimming movement might become 

 modified during growth, in response to changes in body form, modes 

 of feeding and other factors of behavior ; and it is still quite possible 

 that in the adult fish there is a cephalo-caudal ^progression of move- 

 ment which is obscured by other factors of special adaptation. 



This contribution should not be submitted without reference to 

 the splendid work of Paton"^ on the reaction of vertebrate embryos. 

 This is the only paper accessible to me that bears in any respect im- 

 mediately upon the work in hand. Paton's contribution, however, 

 is chiefly upon the development of fishes, "with merely a reference to 

 Rana and Amblystoma, and is particularly devoted to the spontaneous 

 movements. Such movements w^ould seem to be much more common 

 in embryos of fishes than in embryos of Diemyctylus. The latter, 

 during the early phases of irritability to touch, may be under obser- 

 vation for hours without making a perceptible spontaneous move- 

 ment of the trunk, cardiac and branchial movements not being taken 

 into account in my work. 



My approach to the problem of physiologico-anatomical correla- 

 tions in the development of the neuro-muscular system of vertebrates 

 differs materially from that of Paton's method. Paton undertakes 

 "to determine in a general, but not in a specific way" how far the 

 reactions are dependent upon "the functional activity of a nervous 



'"The Reaction of the Vertebrate Embryo and the Associated Changes in the 

 Nervous System." Mittheilungen a. d. zoologischen Station zu Neapel, Bd. 18, 

 Heft 2 n. 3, 1907. 



