CONTROL OF MORPHOGENESIS IN PLANARIA. 323 



water containing CO 2 or in alcohol 1.5 per cent, at the same tem- 

 perature as the control, and under more extreme conditions 

 the teratomorphic, anophthalmic and headless forms appear. 



On the other hand, if we take pieces which show nearly 100 

 per cent, of headless forms in well aerated water at 20 C. we 

 find that similar pieces kept at 30 C. will produce not only 

 anophthalmic, teratomorphic and teratophthalmic heads, but 

 a considerable percentage of normal heads. These illustrations 

 w y ill serve to indicate the general character of the experiments 

 along this line. 



Below are given the results of a few series of experiments 

 on size, region, temperature, alcohol, nutrition and mechanical 

 stimulation. 



I. Size and Region. 



We may investigate these factors by cutting the whole body 

 of worms of the same size and similar condition into one-fourth, 

 one-sixth, one-eighth, one-twelfth and one-sixteenth pieces, 

 etc., and comparing the results. The following table is a part 

 of a series of this kind and shows in somewhat abbreviated form 

 the results for one-eighth and one-sixteenth pieces of large worms. 

 The head is not included and the pieces of the body are numbered 

 consecutively I, 2, 3, etc., from the anterior end backward; the 

 consecutive numbers in the second column refer to the pieces. 

 The remaining columns show the percentages of each of the 

 regulatory types for each set of pieces. In this series each set 

 consisted of only ten pieces, but the results are almost as uniform 

 as in much larger series. 



In this table the factors of size and region appear clearly. We 

 see that the capacity for forming normal wholes decreases pos- 

 teriorly and then in the region of the second zooid increases again 

 suddenly. The anterior ends of the one-eighth pieces respect- 

 ively are at approximately the same levels as those of nos. I, 3, 

 5, 7, 9, n, 13, 15 of the one-sixteenth pieces and it is at once 

 evident that the longer one-eighth pieces possess a greater capac- 

 ity for head formation than the shorter one-sixteenth pieces. 



We can obtain a more striking expression of this fact by com- 

 paring very long and very short pieces from similar worms cut 

 with anterior ends at the same level. One of my series of this 



