Vol. XVI May, 1909. No. 6 



BIOLOGICAL BULLETIN 



THE REGULATORY CHANGE OF SHAPE IN PLAN- 

 ARIA DOROTOCEPHALA. 



C. M. CHILD. 



The recent discovery of Planaria dorotocephala Woodworth 

 (Woodvvorth, '97) in very large numbers, near Chicago, has made 

 it possible for me to use this form for extensive series of experi- 

 ments. The species is very similar to P. niacitlata in structure, 

 behavior and regulation, but possesses some advantages over that 

 species for experimental work. It attains a larger size, is more 

 active, and can be obtained in unlimited numbers and all ages in 

 this locality, while P. macnlata is much less abundant. I found 

 the same species in California some years ago (Child, '06), but 

 was unaware at that time that it had been described. 



In the present paper only certain experiments concerning the 

 effect of anaesthetics on form regulation will be considered. It is 

 possible by the use of dilute solutions of anaesthetics to control, 

 modify and inhibit various regulatory processes almost at pleasure. 

 For example, head-formation can be made a process of redifferentia- 

 tion instead of regeneration in almost any desired degree (Figs. 14 

 and 1 6) or can be completely inhibited, according to the condi- 

 tions of the experiments, and the same is true concerning the 

 formation of a new posterior end and a new pharynx, and the 

 regulatory changes in the intestinal branches. Moreover, the use 

 of anaesthetics permits, in greater or less degree, an analysis of 

 some of the various factors concerned, and finally, it is possible 

 by this means to produce individuals capable of continued exist- 

 ence if returned to water which possess characteristics, or per- 

 haps more properly, combinations of characteristics which do not 

 occur in nature. 



The anaesthetics chiefly employed in my experiments thus far are 



