Harper, Reactions of Penchceta. 



575 



suspended at the more irritable ends it may continue in the middle. 

 And type V indicates that when the whole body is involved most 

 completely in the shrinlving movement extension finds its first outlet 

 at the anterior end. 



Relation to the Musculatu7-e. — Certain anatomical features of the 

 musculature need to be considered in connection with these types 



Ep. 

 C 



L 



Fig. 1. This is to show the extent of circular and longitudinal muscles 

 in different regions. A is from a section through the sixth segment from 

 the anterior end ; M, from a section in the middle region ; P, from a section 

 through the sixth segment from the posterior end; Ep, epidermis; C, circular 

 muscles ; L, longitudinal muscles ; S, muscles of the setae. 



of reaction. A comparison of a section through the sixth segment 

 from the anterior end with sections through the middle and the sixth 

 segment from the posterior end shows that the circular musculature 

 is highly developed in the anterior end, its thickness being twice 

 that in the other regions. The longitudinal musculature is rather 

 uniformly developed throughout the whole length. The reaction 

 of type V involves the completest activity of the whole longitudinal 

 and circular muscular systems, and under these conditions the anterior 



