STRUCTURE AND DEVELOPMENTAL RATE 159 



their several parts to the slow rate in such a manner as to main- 

 tain the normal differences in rate of activity among the several 

 parts. The developmental rhythm of the parts is retained and 

 the proper system of balance is unchanged. On resumption of 

 the normal rate the parts all respond in their usual accord. 

 After a complete interruption in development at a critical stage, 

 on resuming the process those parts or organs that were formerly 

 developing at a rate in excess of the parts in general are unable to 

 start up again with their original excess or advantage and other 

 parts have an opportunity to compete equally with them and 

 may thus cause their reduced or arrested expression. That 

 organ developing at the most rapid rate or having the highest 

 degree of metabolism or oxidation at the time of the stop is less 

 able to initiate its original rate when the moment of resuming 

 development occurs than are those parts that were developing 

 more slowly. 



The production of abnormal development and malformation of 

 organs by treating eggs with strange chemical materials is brought 

 about in a similar manner to the abnormalities following stopping. 

 The part or organ developing at the most rapid rate is inhibited 

 more decidedly by the treatment than are less rapidly developing 

 parts and is, therefore, most affected or modified in its develop- 

 ment. For example, at certain stages, the formation of the optic 

 outpushings from the neural tube is the most energetic process 

 taking place in the embryo. Any injury to the egg at this time 

 works to the particular disadvantage of this process and results 

 in underdeveloped or deformed eyes. If the injurious element is 

 then removed, all other parts may continue their development 

 normally, since they were not sufficiently active at the time of 

 injury to be affected in particular. In other words, all of the 

 other parts were affected similarly and no one was any more 

 inhibited than another. 



The results of slowing and stopping development may be 

 stated very concisely as follows: On slowing development, all 

 parts and organs lower their rates in a somewhat relative fashion, 

 the faster-going parts, even though more decidedly slowed, are 

 still progressing at a faster rate than the slow-going parts. On 



