388 F. H. Krecker, 



somites had been removecl, and tlie entire amount removed was re- 

 generated only when the first somite alone had been cut off. After 4, 

 5 and 6 somites iiad been removed but one half segment was replaced. 

 Beyond a certain level it is usual, of course, for fewer somites to be 

 replaced than have been removed but generally several scmites at 

 least are formed, 3 in Tubifex, 6 — 7 Lumbriculus and 5 in Lumbricus. 



Movement of the Anterior End. 



In the process of procuring worms from the pools some occasio- 

 nally had their heads cut off and it was noticed that several of them 

 lay on top of the mud in the jars without again burrowing into it. Upon 

 examination they were found to have lost the anterior end posterior 

 to ' the 8th somite i. e. posterior to the point where head formation 

 is possible. Lillie (Ol) in some experiments upon Dendrocoelum found 

 that pieces capable of forming a new head behave more like a normal 

 individual than do those not capable of prcducing a head and Child 

 likewise noted the same difference to exist in Lepoplana, Cestoplana 

 and some other Turbellaria. Child (06) thinks such differences in 

 reaction are, to a great extent, due to the physiological character of 

 the part of the nervous System present in this region. In order to 

 discover what difference, if any, exists in the burrowing tendency 

 or capability of headless pieces within and without the head pro- 

 ducing Zone some individuals were beheaded in the former region 

 and otheis in the latter. 



December 12th 08. From ten worms the first two somites were 

 removed and from ten otliers the somites 1 — 10 or 1 — 11 were 

 removed. The animals were then gently placed on the top of soft mud 

 in a dish of water. Two days later nine of the first set had entered 

 the mud and were not visible. The tenth was dead. Nine of the se- 

 cond set were on top of the mud and one was not visible. Those on 

 top moved about very little and did not attempt to bore into the mud. 

 Eight days after the Operation eight of the second set were still on 

 top of the mud and one had partly entered it. Except for the usual 

 waving of the posterior end they were comparatively quiet, but the 

 waving affected the greater part of the body. 



Dec. 18th 08. The first 7 (A), 6 (B), 5 (C), 4 (D) and 3 (E) so- 

 mites respectively were removed, in each case from ten individuals. 

 As before they were all gently placed upon soft mud, each lot in a 

 separate dish of water. Ten days later five of A had disappeared and 

 five had made mud tubes on top of the mud. The latter individuals 



