2O4 C. M. CHILD. 



bring the disc into a completely horizontal position : it always 

 remains somewhat oblique. Contraction at this stage causes the 

 angle between disc and axis to approach its original value, i. e., 

 the disc becomes nearly as oblique as the original cut surface. 

 As time goes on, however, the oriented animal brings the disc 

 more and more nearly into the horizontal position and the 

 obliquity of the disc in the contracted condition gradually de- 

 creases. In the later stages the obliquity is visible only in the 

 contracted condition, the disc being apparently at right angles to 

 the longitudinal axis in the distended oriented specimen. 



This relation between the distended, oriented condition and 

 the contracted condition is characteristic not only for pieces with 

 oblique discs but for various other forms artificially produced. 

 Whenever the artificial form interferes with the orientation a 

 gradual compensatory regulation may be observed. 



The most obvious conclusion and, I think, the correct one, 

 regarding the regulation of the oblique discs is that the changes 

 in the body-wall of the two sides of the body occur in conse- 

 quence of the characteristic functional condition of the muscles. 

 The muscles beneath the upper side of the disc being continually 

 more or less contracted undergo a " functional " change in struc- 

 ture and lose a part of their original power of extension, while 

 the muscles beneath the lower edge of the disc, being continually 

 highly extended lose to some extent their original power of con- 

 traction. Or, considered from another point of view, there is 

 functional atrophy on one side and functional hypertrophy on 

 the other. The ectoderm and the entoderm of the body-wall 

 follow these changes by similar growth or reduction. With each 

 change further change becomes possible until the animal is 

 finally able to orient itself in the typical manner, or in other 

 words has attained the typical form. The most important point 

 in this interpretation is the role played by the efforts of the 

 animal to carry on its typical activities. In my opinion these 

 efforts are the cause of the regulation. The animal attempts to 

 perform certain acts and certain resulting conditions of the tissues 

 give rise to a certain form. The reaction or attempt at reaction 

 produces the form incidentally. The typical form is then in this 

 sense the result, not the cause of the typical reaction. 



