THE ORIGIN OF THE NERVOUS SYSTEM 145 



connection with the musculature has been advocated by Claus (1878) 

 and by Chun (1880), but a nervous system without effectors is, as 

 Samassa (1892) and Schaeppi (1904) declare, scarcely conceivable. 



The opinion about the origin of nervous and muscular tissues as 

 expressed in these articles is opposed to the various theories stated in 

 the preceding paragraphs in that muscular tissue is regarded as- the 

 ancestral tissue and nervous tissue is supposed to have formed sec- 

 ondarily and as a means of bringing muscular tissue into action with 

 greater certainty than direct stimulation would do. According to this 

 view the primitive state of the neuromuscular mechanism is to be seen 

 in such animals as sponges, which possess muscles but no true nervous 

 organs; and the neuromuscular or, better, epithelial-muscular cells of 

 the ccelenterates represent these primitive effectors to which have been 

 added a diffuse system of receptors as seen in the sea-anemones or a 

 specialized system as in the jellyfishes. In both instances the receptors 

 and effectors are related through a nervous net. 



References 

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