140 



REGENERA TION 



appear to belong to the same category as those described above for 

 adult forms especially in those cases where pieces regenerate by 

 morphallaxis. 



In connection with the production of double structures there 

 should be mentioned a peculiar method of formation of new heads, 

 first discovered by Van Duyne in a planarian. He found that if the 



B 



FlG. 44. A. Planaria lugubris, cut in two as far forward as region between eyes, regenerating 

 half-heads. B. Same cut in two at one side of middle line. Smaller piece produced a new 

 head. C. Planaria maculata, split in two. It produced two heads in angle. D. Another, 

 that produced a single head in angle. 



animal is cut in two in the middle line, the halves being left united 

 only at the head-end, as shown in Fig. 44, D, C, there may appear one 

 or two new heads in the angle between the halves. I have repeated 

 this experiment with the same result, and have found that it may also 

 occur when only a piece is partially split from the side of the body, 

 as shown in Fig. 44, B. In Van Duyne' s experiment the two new 





