CHAPTER XVI 



THE PROTOZOA IN CONNECTION WITH 

 MORPHOGENETIC PROBLEMS 



Francis M. Summers 



The quest for underlying causes of organic unity or individuality has 

 been for many years one of the most intriguing and, at the same time, 

 one of the most evasive problems in experimental biology. That an im- 

 mense amount of work, involving a large variety of organisms, has pro- 

 duced little more than a background for what may be the ultimate 

 solution is neither surprising nor discouraging. If analytical research 

 cannot now detail all of the vital processes, then what progress should 

 be expected in the full appreciation of the total relations between them? 



One of the principal approaches to the evaluation of factors which 

 condition growth and development is through studies of regeneration. 

 This method consists essentially in disturbing the normal trend of de- 

 velopment in order to obtain unusual or exaggerated expressions of one 

 or more of the growth-conditioning or integrating factors. The fact that 

 a fragment of an organism is frequently capable of regenerating a com- 

 plete organism the total characteristics of which are homologous with 

 those of the original is convincing evidence that some kind of funda- 

 mental organization characterizes the fragment and is responsible for the 

 individuality of the new organism derived from it. Conversely, regional 

 specialization or localization in the regenerating fragment presupposes 

 the existence of overlying control mechanisms, i.e., the operation of 

 factors or a set of energy transformations which restrict, direct, or deter- 

 mine the complete developmental freedom of its various parts or regions. 

 If some such hypothesis of energy changes and translocations serves to 

 fix our experimental point of view, then the many fragmentary accounts 

 and dangling issues herein reported may serve as a challenge to those 

 who are acquiring the newer instruments and techniques provided by the 

 sciences. 



In common with other organisms, the Protozoa exhibit such features 



