CHAPTER IV 



INDEPENDENT EFFECTORS IN HIGHER 



ANIMALS 



IF sponges possess effectors, such as muscular sphinc- 

 ters, that are not innervated, but that become active in 

 consequence of direct stimulation, and if these animals 

 exhibit at best a low degree of transmission such as that 

 designated as neuroid, it is not improbable that these con- 

 ditions may persist locally or be revived in the organiza- 

 tion of the more differentiated animals. At least a search 

 for such instances may not be an unprofitable one. 



From the standpoint of musculature it may be asked 

 whether the more differentiated animals possess muscles 

 that are directly stimulated normally or, to go one step 

 further, that act with complete independence of nervous 

 control! Such muscles would simulate in many respects 

 those believed to exist in sponges. Evidence in favor of 

 this possibility has been brought forward within recent 

 years in connection with the sphincter of the vertebrate 

 iris. The contraction of the pupil of the eye in bright 

 light is a well-attested fact and has long been recognized 

 as an example of simple reflex action in which the afferent 

 course is through the optic nerve and the efferent one 

 through the oculomotor nerve. Nevertheless, the sphinc- 

 ter of the pupil also seems to act under direct stimulation. 



Arnold, as early as 1841, observed that in the eye of 

 the eel the pupil contracted in bright light even after that 

 organ had been removed from the fish's head. And 

 Brown-Sequard subsequently confirmed this observation 

 and showed that when the eye was cut in half vertically, 



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