MOVEMENTS, ETC., OF FKESH-WATEU PLANAKIANS. 575 



fuiictiou of the brain of Plauaria witli reference to move- 

 ments is to maintain the tonus of the ciliary system. That 

 neither the crawling nor the gliding movements are specific 

 functions of the central nervous system is evident,, because 

 both sorts of movement may take place after its removal. 

 Yet all my observations tend to show that after injury to or 

 loss of the brain the gliding movement becomes^ almost 

 immediately, markedly slower. This relation is especially 

 well indicated by the experiments noted above on splitting 

 the animal longitudinally from the anterior and the posterior 

 ends. In the one case the gliding movement becomes at 

 once distinctly slower, while in the other case there is only a 

 slight difference in the rate, evidently conditioned by the 

 fact that only comparatively few of the cilia can get a hold, 

 so to speak, so that they can function. The force of the 

 argument will be impressed if one glances at the relative size 

 of the cuts in Figs. 12 and 13, and then remembers that the 

 rate of gliding of the specimen figured in Fig. 13 is faster 

 than that of the one in Fig. 12. With the co-ordination of 

 movements, including the crawling, the central nervous 

 system has very little to do in the case of Planaria. With 

 regard to the spontaneity of movement it is difiicult to decide 

 in how far the brain functions. It is certain that regenerat- 

 ing anterior pieces show more spontaneous movement than 

 do posterior pieces, yet the anterior pieces are behind the 

 normal worm in this respect. The brain probably plays 

 some part in the performance of normal spontaneous move- 

 ments, but, as has been pointed out, in these operation 

 experiments the whole matter is very definitely related to 

 the regenerative process, and loss of substance plays nearly, 

 if not quite as great a part as loss of nervous system. 



Summarising, we may say that — 1. For the performance 

 of the crawling or gliding movements the brain is not specifi- 

 cally necessary. These movements are normally co-ordinated 

 in the absence of the brain. 



2. The maintenance of the tonus of the ciliary system 

 (which produces the gliding movement) is a specific function 



