276 C. M. CHILD 



In all such series of pieces the factors of length of piece and 

 region of body from which it is taken are both involved, but it 

 is possible to separate them more or less completely by comparing 

 on the one hand pieces of the same size from different regions 

 of the body, and on the other, pieces of different size from as 

 nearly as possible corresponding regions. The present paper is 

 devoted chiefly to experiments of this character. In following 

 papers the effect of various external and iniernal factors in modi- 

 fying the course and result of regulation will be considered. 

 This whole series of experiments is preliminary to further inves- 

 tigation and a full statement of results is desirable at this time 

 both because the results are of interest in themselves as a contri- 

 bution to our knowledge of regulation, and also because they, 

 or some of them possess, as I believe, a certain general and theo- 

 retical significance. 



2. The chief differences in the course and results of regulation 



of pieces 



As the first step in our consideration it is necessary to describe 

 briefly the general course of regulation, its variations and their 

 limits and the character of the results for pieces of different 

 size and position. We already possess some data upon this point 

 from the work of Morgan and others, and I have considered the 

 subject briefly in an earlier paper (Child, '0Gb). It will be evi- 

 dent, from this and the following sections that Morgan failed 

 entirely to understand the significance of certain of the differ- 

 ences in regulation which have to do with the size of the pieces 

 and the region of the body from which they are taken. 



In the study of thousands of pieces of different size and from 

 different regions of the body I have found that they fall most 

 naturally as regards the course and results of regulation into 

 six groups or categories. I refer here of course merely to com- 

 pletely isolated pieces including the whole width of the body, 

 and not to the various types of double and multiaxial forms 

 which result from various methods of partial isolation, unilateral 

 isolation, etc. All of these groups have been observed and men- 



