NEUROID TRANSMISSION 65 



of these elements has been carried out by Saguchi (1917). 

 Some of the earlier workers advanced the opinion that 

 at least among certain, invertebrates cilia were under the 

 control of the nervous system, and Apathy (1897) went so 

 far as to claim that the intracellular fibrillar system of 

 the ciliated cell was nervous, though he never succeeded 

 in demonstrating a connection between this system and 

 nerves. The fact, however, that no one has ever been 

 able to control ciliary activity through nerves and that all 

 the cases of ciliary coordination thus far brought for- 

 ward can be explained on the basis of neuroid transmis- 

 sion renders the belief in the nervous control of cilia ex- 

 tremely improbable. In fact, it may be stated that at 

 present there is not the least ground for the assumption 

 that true nervous activity is in any direct way involved 

 in ordinary ciliary reactions. Yet notwithstanding this 

 independence of ciliated and nervous tissues, the coor- 

 dination in the activities of a ciliated field is one of its 

 most striking features. 



If the ciliated epithelium from the palate of the frog 

 is placed under a microscope, the various foreign par- 

 ticles lying on its surface will be seen to be swept along 

 in a definite and constant direction, in this particular in- 

 stance toward the oasophageal end of the tissue. The 

 ciliated field, moreover, will reproduce in its appear- 

 ance almost exactly the aspect of a field of grain over 

 which a gentle wind is blowing. The direction of the 

 undulations in this field agrees with that in which the 

 particles are borne along. 



When these appearances are further examined, they 



are found to depend upon two factors, the direction of the 



effective stroke of the cilia and the sequence of these 



strokes. The direction in which the particles move is 



5 



