THE NEQROMUSCULAR STRUCTURE 83 



worked out, the presence of nervous elements in these 

 animals is beyond dispute. 



The effector systems of sea-anemones, as might be 

 expected, are more numerous and complicated than those 

 in sponges. Sea-anemones possess at least four systems 

 of effectors: mucous glands, ciliated epithelia, nemato- 

 cysts, and muscles. 



There has never been any ground for the assumption 

 that the mucous glands and the cilia in coelenterates are 

 under nervous control. These effectors respond only to 

 direct stimulation and are not open to influences from 

 a distance. Even in the case of such coelenterate cilia as 

 those of the lips of actinians where by appropriate stim- 

 ulation a reversal of the effective stroke can be brought 

 about (Parker, 1896, 1905 a; Vignon, 1901), the whole 

 reaction is so strictly local that there is not the least 

 reason to assume the intervention of nerves. The mucous 

 glands and cilia, therefore, bear all the marks of indepen- 

 dent effectors and hence free from nervous control. 



The nettle cells with their contained nematocysts, on 

 the other hand, have often been regarded as subject to 

 nervous influence. Schulze, who studied these cells in 

 Cordylophora with great care in 1871, showed that each 

 one was provided with a special bristle-like projection, a 

 cnidocil, by which it could be stimulated directly, and 

 argued from this that in their action they were indepen- 

 dent of the nervous system. Nevertheless the discovery 

 by the Hertwigs (1879-1880) that their basal processes 

 branched as those of the sensory cells did, led these and 

 many other investigators to believe that the nettle cells 

 had nervous connections. This opinion has been ex- 

 pressed even as recently as 1913 by Baglioni. There is, 

 however, not the least experimental ground for assum- 



