278 C. M. CHILD 



like fig. 3, on the other liand, the head develops slowly and 

 remains of relatively small size, the movements of the piece are 

 much less rapid and the margins of the posterior half or more of 

 the body are used for attachment. Consequently the elongation 

 and decrease in width of the body occurs most rapidly in the 

 anterior region. In cases like fig. 2, which are intermediate in 

 character between the extremes of figs. 1 and 3 the processes 

 of elongation and change of shape show, like the other processes, 

 a course intermediate between the extremes. 



From these normal wholes we find the character of the pieces 

 diverging in two directions, first toward headlessness, the whole — 

 headless series; and second toward taillessness the whole — 

 tailless series. 



Wholes with abnormal eyes ^ Teratopthalmic wholes.' These 

 are intermediate between normal wholes and headless forms 

 The frequent occurrence of abnormalities of the eye spots in 

 the regulation of pieces of Planaria has been noted by various 

 authors, but the conditions of their appearance have not been 

 determined. I have distinguished these wholes with abnormal 

 eyes as a separate group because, as will appear below, they 

 stand between the normal wholes and the third group and because 

 their appearance can be controlled experimentally to a large ex- 

 tent. The teratopthalmic wholes usually do not differ essentially 

 as regards the changes of shape and proportions, the relations of 

 new and old tissues etc. from the normal wholes, except that abnor- 

 mal eyes are of much less frequent occurrence in pieces which 

 develop large heads like fig. 1 than in others, though even in 

 such pieces their frequency may be altered by various external 

 factors and so experimentally controlled. In general it maybe 

 said that the larger the head produced by the piece, the greater 

 the frequency of normal eyes and vice versa. Many teratop- 

 thalmic wholes differ visibly from normal wholes only as regards 

 the eyes (fig. 4), but in extreme cases the head is very small and 

 develops very slowly (fig. 5). 



The nature of the abnormalities differs widely in different cases : 

 Fig. 6 shows a few characteristic cases. Abnormalities of position 

 and size are shown in fig. 6, a, b, c ; abnormalities of number in d, e, 



