DYNAMICS OF MORPHOGENESIS 167 



of disintegration are unsatisfactory here because in many cases 

 disintegration involves certain regions, days or weeks before it 

 does others and sometimes it involves only those regions of the 

 body having the lowest rate of reaction, i.e., the posterior region 

 of the first zooid, and the body may separate into two pieces, 

 which then undergo some degree of regulation and attain a some- 

 what higher rate of reaction. In other words, disintegration is 

 often only partial and does not necessarily lead at once to the 

 death of the whole. For these reasons it has been found best 

 to record at each observation merely the number of individuals 

 which remain intact. 



These records can be most readily presented in graphic form 

 as in m}'' earlier paper (Child '11 a). Figure 1 is a reproduction 

 of figure 2 of that paper. The starting point a of the curves of 

 the axis of ordinates represents 100 per cent of the number of 

 worms used, each small space of the cross section paper along the 

 axis of ordinate representing 2 per cent of the total. 



Along the axis of abscissae each small space of the paper repre- 

 sents one day. The ordinates of the various points of the curves 

 show the percentage of worms intact at any time during the exper- 

 iment, the curves being plotted from observations forty-eight 

 hours apart. 



In figure 1, the curve ah represents the resistance to 1.5 per 

 cent alcohol of fifty physiologically old worms 20 to 25 mm. in 

 length, the curve ac, the resistance of fifty younger worms 12 to 15 

 mm. in length. These results can also of course be tabulated in 

 numerical form. 



III. THE EVIDENCE FOR THE RELATION BETWEEN RESISTANCE 

 TO DEPRESSING AGENTS AND RATE OF REACTION 



1. Resistance and stimulation 



One of the simplest ways of demonstrating the relation between 

 the physiological resistance to a given reagent and the rate of 

 reaction is the comparison of stimulated and unstimulated animals. 

 Various possibilities are open here, the increase in rate of reaction 

 following a cut or a sudden change of temperature, mechanical 

 stimulation, etc., may with proper care be demonstrated. But 



