STUDIES ON THE DYNAMICS OF MORPHOGENESIS 275 



In the study of the factors of size and region two methods of 

 section were chiefly employed. One of these, most used in earlier 

 experiments, consists of simply cutting the body, beginning at 

 one end, into successive pieces as nearly as possible equal in 

 length, and recording the result for each piece. It is impossible, 

 how^ever, with this method to avoid very considerable differences 

 in size of different pieces, consequently in later experiments a 

 somewhat different method was employed which gives much more 

 satisfactory results as regards uniformity of length. This method 

 consists in cutting the body into halves or thirds and then halving 

 each of the pieces thus obtained and the resulting pieces again or 

 even a third time if desirable. It is much less difficult to divide 

 a given piece into approximately equal parts than it is to cut 

 successive pieces of the same length from one end of an animal. 



In a large number of my experiments each individual piece 

 was isolated in a dish and a separate record kept for it. These 

 experiments were of great value for they enabled me to distin- 

 guish certain differences in individuals which would scarcely 

 have been noted otherwise. But after some of the factors 

 which determined these differences were recognized and it became 

 possible to select with a fair degree of accuracy worms which were 

 in the same or nearly the same physiological condition, it became 

 desirable to obtain more general expressions for the differences 

 correlated with differences in length of piece and region of body. 

 To obtain such results each of a number of worms of the same 

 size and as nearly as possible in the same condition was cut into 

 the same number of pieces and all corresponding pieces were 

 placed together. In such series a record was made for each piece, 

 but there was nothing to show which pieces in two different sets 

 belonged to the same individual worm. This method has the 

 advantage, however, that it permits compact and relatively 

 exact expression of the results, as the tables and curves will show. 

 The data considered in the present paper are all obtained by 

 this second method of experiment, though many other 'individ- 

 ual series' might have been added, since they give the same 

 results, except for the greater irregularity consequent upon the 

 method of operation. 



