282 



A. S. PEAKSE. 



what to conform to the bilateral plan of structure and, as the 

 radial nerv^es are not equally well developed, there is a dorso- 

 ventral as well as an antero-posterior differentiation. In order to 

 test the reactions of fragments of the body a series of experi- 

 ments was carried out in which twelve TJiyoncs were each divided 

 into two approximately equal pieces by a transverse cut. The 

 two pieces of each animal were laid in a dish of sea water before 

 a window in the position shown in Fig. 6. The ventral side of 



^ 



> 



> 



Fig. 6. Diagram to show the position in which animals were placed in the dish 

 after being cut in two. The arrows represent the direction of the light, a, anterior 

 end ; /, posterior end. 



the body was always placed uppermost and the long axis of the 

 body was at right angles to the direction of the rays of light. 

 The movements of the two halves were observed during the three 

 hours following their separation and a summary of these reactions 

 is given in Table III. Although the tube-feet were more or less 



Table III. 



Showing the number of anterior and posterior halves of twelve Thyoncs which 

 gave different reactions. 



active on both halves of the body in all cases, it will be seen that 

 the posterior halves gave characteristic reactions more often than 

 the anterior portions. They carried on normal spouting move- 



