ANALYSIS OF FORM REGULATION. I /I 



ing a new animal in anaesthetics, as we can readily show by iso- 

 lating it physically, i. e., by cutting it out and placing it in an 

 anaesthetic medium, where it almost always degenerates. Con- 

 sequently its condition while still attached to the other parts is 

 comparable to its condition when physically isolated, i. e., it is 

 then physiologically isolated to such a degree that it behaves as 

 if physically isolated and disintegrates. When we add the effect 

 of low temperature to that of the anaesthetic, the physiological 

 isolation is more certainly and more completely induced, con- 

 sequently disintegration of this region is more frequent in low 

 temperatures. This process of disintegration does not occur in 

 small individuals because they are far below the limit of size and 

 the posterior end of the first zooid is not physiologically isolated 

 in anaesthetics to any such degree as in the larger individuals. 



VIII. Acclimatization. 

 If the individuals or pieces live for a week or more in the 

 anaesthetic they became more or less acclimated and begin to 

 move about and react in the usual manner, though very slowly 

 and imperfectly. In many cases they continue to live for months, 

 especially in alcohol. In ether and chloretone I have not as yet 

 been able to keep them alive for so long a time in concentrations 

 corresponding in their effect on regulation to those of alcohol 

 employed for this purpose. By beginning with mixtures of low 

 concentration and gradually increasing the concentration they 

 can be acclimated to concentrations which otherwise kill them 

 within a few hours. I have not thus far attempted to determine 

 the limit of acclimatization, since my attention has been 

 directed chiefly to other problems. It is of interest, however, to 

 note that young animals become more readily and more com- 

 pletely acclimated to mixtures of given concentration than do 

 older ones, although the younger individuals show a higher 

 death-rate than the older when first placed v, the anaesthetic. 

 And finally individuals which have been re 'uced in size by 

 starvation do not show the same power of acclimatization as 

 young animals of the same size, but on the contrary, their ability 

 to become acclimated decreases as starvation and the decrease in 

 size continue. These facts bear upon various recent attempts at 



