Studies on Regulation. 529 



is incapable of more than a very slight degree of attachment. In 

 the absence of the mechanical tension to which the tissues are 

 normally subjected, the apparent reduction in size of these pieces 

 is considerable (compare the posterior part of Fig. 27 with Fig. 40. 

 See also Child, '02). This apparent reduction is due in part to 

 altered physical conditions, for the decrease in the longitudinal 

 and transverse diameters is accompanied by a relative increase 

 in the dorso-ventral diameter. In general the same parallelism 

 between motor activity and regenerative power is found in these 

 pieces from different regions as in those already described. 



Brief mention must be made of a few special cases of anterior 

 regeneration which differ in certain respects from the average. 

 Groups of eye-spots appear occasionallyin the new tissue of 

 posterior pieces not only when the plane of section is immediately 

 posterior to the ganglia as in piece A, Series 71 (p. 522) but even at 

 levels as far back as the anterior end of the pharynx. Except 

 where the plane of section is very near the ganglia the eye-spots 

 appear only after two or three months. In Fig. 41 a case of this 

 sort is shown; here the cut was made at the level of the anterior 

 end of the pharynx and the eyes were first observed two and one- 

 half months after section. Other cases do not differ essentially; 

 sometimes only one or two eye-spots appear and sometimes two 

 or three groups of them are visible. It is probable that outgrowth 

 of nerves from the cut ends of the nerve cords is responsible for 

 the formation of these structures. If this is the case it is an inter- 

 esting fact that the eye-spots are developed in such cases in con- 

 nection with a part of the nervous system different from that with 

 which these organs are usually connected. This is another bit 

 of evidence in favor of the view that the differences between 

 different regions of the central nervous system are differences of 

 degree rather than of kind. Regions of the body posterior to the 

 anterior end of the pharynx have never been seen to produce eye- 

 spots; on the other hand they are most common in pieces like 

 A, Series 71, from which only the ganglia have been removed. 

 The frequency of regeneration of these organs decreases poste- 

 riorly like the power of regeneration and of motor activity. Prob- 

 ably these organs are the result of a direct influence of the nervous 



