98 'Journal of Co^nparative Neurology and Psychology. 



It would be a difficult thing ordinarily to demonstrate that the recep- 

 tive fields and afferent conductors become functional in an embryo 

 before the effectors do, for through the effectors alone is the func- 

 tioning of the receptor and conductor demonstrable. But if the skin 

 of a given somite in the tail bud of an amphibian embryo of suitable 

 age be touched there will be no perceptible response in the effectors 

 of that segment, while response will occur in the older somites farther 

 cephalad. Into this given caudal somite, then, impulses are pouring 

 from the external world through the receptors and conductors before 

 the effectors of that segment are capable of making any perceptible 

 response whatever. If this is tiiie of the more caudal somites, it 

 may be assumed to be true of the head seginents also, and the embryo 

 may be regarded as existing under a storm of impulses of the receptive 

 system for a considerable period before it has the ability to give ex- 

 pression through its effectors. Hovv widely this order of development 

 of the receptor and effector may be applicable, as a law, and what its 

 significance may be are questions of interest. It is possible that the 

 summation of subliminal stimuli in neuro-musc\iIar reflexes rests 

 upon this as a fundamental principle of functional development. 

 It is possible, also, that Kappers^ might correlate this precocity of 

 the afferent system with his theory of neurobiotaxis, in which he 

 assumes that the afferent conductors have influence over the effector 

 centers to cause them to migrate, phylogenetically at least, in the 

 direction of the maximal amount of stimulation. 



The Swimming Movement. 



The movements of Diemyctylus embryos are of two main types ; 

 (1) the flexure, which is a bending of the body in one direction 



""Phylogenetisclie Yerlagerungeu der motorisehen Oblongatakerne, ilire 

 Ursaclie und Bedeutuug." Neurol. Centralbl., No. 18, 1907. 



"Weitere Mitteiluugeii beziiglicli der pliylogenetiscben Veiingoruiig der 

 iiiotoriscben Hirunervenkerue. Der Bau des antouonien Systenies." Folia 

 Neuro-Biologiea, B. 1, Nr. 2, Jan., 1008. 



"Weitere Mitteiluugeii fiber Neurobiotaxis." Folia Neuro-Biologiea, B. 1, 

 Nr. 4, 1908. 



"The Structure of the Autouoniic Nervou.s System compared with its 

 Functional Activity." Journal of I'hysiology, Vol. XXXVII, No. 2, 1908. 



