540 C. M. Child. 



Regeneration after longitudinal section near the median plane 

 and regeneration of small lateral pieces present some features of 

 interest; a description of cases of each kind is accordingly given. 



Series 64. A large specimen was sectioned longitudinally 

 slightly to the left of the median plane (Fig. 56). The plane of 

 section passed through the left cephalic ganglion, leaving only a 

 small portion of the ganglion together with most of the eyes in the 

 left piece. After section both pieces underwent considerable 

 contraction, but the left much more than the right. The two 

 pieces differed widely as regards behavior; the right piece, con- 

 taining nearly all the ganglionic tissue, behaved like a normal 

 animal, advancing rapidly and using the margin of the head in 

 the characteristic manner. The left piece, on the other hand, 

 behaved essentially like a piece without ganglia. It never became 

 extended, did not adhere closely to the substratum, all movements 

 were slow and the head region showed none of the characteristic 

 motor activity of normal animals. The pieces were examined at 

 intervals of from seven to ten days. 



The most conspicuous difference between the two pieces is the 

 difference in form (compare Figs. 57 and 58). The right piece 

 is much contracted and bent toward the left by the reduction of 

 the cut surface, but the left piece is contracted into almost circular 

 form with the cut surface greatly reduced. Both pieces move in 

 circles in consequence of the form but the radius of the circles 

 described by the right piece is much greater than in the left piece, 

 which simply revolves in a space scarcely greater than its own 

 diameter. 



The difference in form and consequently the difference in 

 direction of movement is of course the direct result of the widely 

 different degree of contraction in the two pieces; and this difference 

 in contraction is undoubtedly due in large part if not wholly to the 

 differences in motor activity in the two pieces; and finally the 

 differences in motor activity depend essentially upon the distribu- 

 tion of the tissue of the cephalic ganglia between the two pieces. 

 The right piece creeps about like a normal animal holding to the 

 substratum by means of the margin and posterior end; thus the 

 body of this piece is subjected to the characteristic longitudinal 



