Sonie Plionointma of Regeneration in Lininodrilus and related Forma. 389 



were not veiy active. All of B, C, and E had disappeared. Seven of 

 D had also gone while three had made mud tubes on top of the raud. 

 Ten days after the Operation three of A were still on top and all the 

 rest, B to E, had gone. 



Level A represents the 8th somite from the anterior end and this 

 is on the border line between those regions which produce a head and 

 those which do not produce one, therefore if lack of proper nervous 

 reaction prevents the worms from burrowing it might be assumed 

 that the three from this level which did not burrow had not sufficient 

 nervous reaction of the proper kind. It is true that both in these ex- 

 periments as well as in the course of numerous experiments conducted 

 for other purposes Worms (Limnodrilus and Tuhifex) deprived of an- 

 terior somites posterior to the head forming level did not move about 

 as much nor as normally as did those not deprived of so many somites. 

 The latter individuals crawled about with comparative activity and 

 usually not in an aimless manner, this reaction being more normal 

 the fewer the anterior somites that had been removed. However it 

 is possible that other factors in addition to proper nervous correlation 

 may render the worms incapable of burrowing. For instance, when 

 somites are removed the anterior cut surface of the remaining portion 

 contracts, so that the body wall bends toward the median line and closes 

 the wound with the result that the anterior surface is almost if not quite 

 flat. Posterior to the 8th somite so long as the worm is quiet the ante- 

 rior end usually remains flat or eise somewhat rounded and when 



the Worm moves in an anterior 



direction the anterior end does not 



become sharply pointed but at most 



slightly rounded. At the 8th somite 



the same is frequently true until new l 2 



tissue is formed. Anterior to the 8th Textfigure 1. 



somite when the worm moves forward ] '^f «^'^f ^ an anterior surface posterior 



to the 8th somite when a worm is at rest 

 its anterior end is COnsiderably pO- and 2 represents the same Individual when 



inted SOOn after an Operation and the '' "oves forward;^ shows an anterior sur- 



^ _ face ui front of the 8th sonnte when the 



more rapid growth of new tissue worm Is in motion and before the prosto- 



here also aids in making this end '"""" '^ •""''"*^^'^= ^ iiiustrates the normal 



'^ condition. 



pointed. 



The accompanying text figures diagrammatically illustrate con- 

 ditions at the anterior end. 



Although lack of movements proper to the head end may in part 

 prevent the worm from burrowing, it seems probably that it is also 



