1 1 8 Herbert Eugene Walter 



6 



a General Form of the Body 



A normal, full-grown planarian may be expected to give typ- 

 ical reactions to any stimulus. Fragments of a planarian, on the 

 other hand, whether occurring from natural or artificial causes, 

 would not be expected to behave as perfectly developed worms 

 do, and observation shows that they do not. 



As previously mentioned, Loeb ('94), and later other investi- 

 gators, established the fact that planarians with eyes and brain 

 removed are still able to give characteristic reactions to light, 

 while Lillie ('01) found that any fragment capable of regenera- 

 tion would respond to light. 



In all cases of mutilated worms, however, the response to light 

 is slower and less precise than that exhibited by normal individ- 

 uals, and therefore different in degree if not in character from 

 that of the latter. It has been repeatedly observed that worms 

 mutilated unilaterally perform circus movements regardless of 

 the light. This seems to be a plain case of morphological limi- 

 tations on the part of the crippled animal, whereby the cilia and 

 musculature of one side, on account of injury, are less efficient 

 than those on the other side. Since it is practically impossible in 

 nature to select at random a dozen planarians of which at least 

 one specimen does not show some sort of mutilation, the modi- 

 fied behavior of morphologically imperfect animals becomes a 

 factor of considerable importance in any general analysis of 

 planarian activities. 



Again, with regard to the general form of the body, it seems 

 reasonable to suppose that a mature planarian loaded down with 

 sexual products, or one gorged with food, must encounter mechan- 

 ical difficulties in responding to light, so far at least as locomotion 

 is concerned, which the same animal when unencumbered would 

 not experience. A few experiments were performed to test this 

 supposition, in which a comparison of the behavior of large and 

 small worms was attempted. Pearl ('03, p. 546), it will be recalled, 

 has shown that in the case of Planaria maculata, a worm 11 mm. 

 long travels at a faster rate than one 6 mm. long. This experi- 

 ment was repeated with a confirmatory result but, as will be seen 



