4 Charles Zeleny. 



It is the plan of the present paper to take up the different 

 groups of experiments on compensatory regulation in turn and 

 to connect them by a final general discussion. The individual 

 groups of experiments are thus quite independent in the descrip- 

 tive portion. 



The work was carried on at the Woods Hole Biological Labora- 

 tory in the summer of IQOI, at the Cold Spring Harbor Laboratory 

 in 1902, and at the Naples Zoological Station from September, 

 1902, to June, 1903. I wish to express my great obligation to 

 Prof. C. B. Davenport, to Prof. E. B. Wilson and to Prof. T. H. 

 Morgan, for inspiration and aid in carrying out the work, and to 

 the members of the staffs at the three laboratories where it was 

 done, for their uniform kindness in giving every convenience in the 

 course of the mvestigation. 



The data will be considered in five sections as follows: 



I. In the first section (p. 5) the experiments on the leaflets of 

 the compound leaf will be briefly referred to as constituting a case 

 of regulation of a system in which there is no regeneration of the 

 removed part. The readjustment is here confined to the unin- 

 jured portions and the assumption of an interaction between the 

 members of the leaf constitutes an important factor in the explana- 

 tion of the changes that take place. 



II. In the second section (p. 7) the rate of regeneration of the 

 arms of the brittle-star, Ophioglypha, is taken up and studied with 

 special reference to the influence which parts of the animal away 

 from the mjured surface have upon the nature of the regeneration 

 at that surface. 



III. The third section (p. 18) consists of experiments on the 

 opercula of the Serpulids made with a view to the analysis of the 

 factors involved in the control of the asymmetry of these animals. 

 Observations on the comparative anatomy of the opercula and 

 on their ontogenetic development made with special reference to 

 the problem of compensatory regulation are included. 



IV. The fourth section (p. 77) contains observations on the 

 regulation of the rate of differentiation in the regeneration of the 

 opercula of the Serpulid, Apomatus ampullifera. The influence 

 of the removal of the posterior part of the body upon the opercula 

 is taken up. The experiments are put into a section separate from 

 the main one on the opercula of Serpulids because they are not 

 directly concerned with the interaction of the 'two lateral sides of 



