iv] SENSE ORGANS AND SENSES 69 



have shown that this is not the case, and that 

 all of the body is sensitive. This disposes of course 

 of the existence of special light-receiving organs in 

 the anterior part of the worm's body. Not only this, 

 but an interesting extension of the view has been 

 promulgated. It has been shown by Prof. G. Parker 

 and a colleague that in the common Brandling worm, 

 Allolobopliora foetida, the response to light stimuli 

 was related to the amount of the body exposed to its 

 influence. This is very important as showing that 

 the light perception in these creatures is probably 

 not due to special organs having a limited position 

 on the body, but is due to collective sense impressions 

 of many cells scattered over the whole body, the 

 impression being the greater when the whole body 

 is exposed and less when only parts of it are exposed. 

 Furthermore, and this has quite another importance, 

 these observers noted that the reaction effects differed 

 when only a part of the body was exposed ; that they 

 were greater in the front of the body, less in the 

 middle, and less still at the tail end. Indeed they 

 found that the reactions in the case of the front end 

 of the body alone being exposed were rather more 

 than one-third as compared with those which were 

 shown when the whole body was subjected to the 

 light stimulus. The fact that the least sensitive 

 region of the body is the posterior end has, it is 

 true, only been definitely proved in the case of the 



