by G.H. P,rkr 



CHAPTER V 



NEUROID TRANSMISSION IN HIGHER ANIMALS 



ALTHOUGH sponges give no evidence of possessing any 

 true nervous tissue and have at most only independent 

 effectors in the form of muscles, it would be a mistake to 

 assume that they are devoid of everything that is in any 

 sense nervous in nature. It has already been pointed out 

 that if a finger of the sponge Stylotella is cut into within 

 a centimeter and a half of the osculum, this aperture will 

 usually close after some minutes. The sluggish transmis- 

 sion upon which this reaction depends represents without 

 doubt that elemental property of protoplasmic transmis- 

 sion from which true nervous activity has been evolved. 

 It may, therefore, not inappropriately be called neuroid 

 transmission. This elemental type of transmission prob- 

 ably occurs in many tissues of the higher animals, but it 

 is by no means easily detected, for most tissues are inca- 

 pable of those activities by which such transmission could 

 be indicated. Favorable conditions for its study, how- 

 ever, are found in one type of epithelial tissue, namely, 

 ciliated epithelium. This tissue is not only freely open 

 to stimulation, but it possesses in its cilia convenient parts 

 of an effector kind by which its responses to stimulation 

 can be shown. Extended ciliated fields are, therefore, 

 favorable grounds for the study of neuroid transmission. 



The structure and function of ciliated cells and epi- 

 thelia have been reviewed recently by Putter (1903), by 

 du Bois-Reymond (1914), and especially by Prenant 

 (1912-1914), and an extensive and original investigation 



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