30-2 F, H. Kreokor. 



sizo iox tho fiftli lovol itithroo somitos i. e. 5 — 7 and it is a shorter pieoo 

 than tliat rcquired at any other level therefore it is tlie sliortest piooo 

 of this worin oapablo of regeneration. Tims far tlie posterior liiuit 

 of tho pitvos has boon at about tlio 7th somite in all of tlio pieces. tlie 

 differenoo botween differont pieces being duo to a varying number of 

 anterior somites removed. Posterior to tlie 5tli soinite tlie ininiber of 

 somitos required inoreases. In tlie pieces anterior to and incliiding 5 — 7 

 posterior regeneration has not been rapid and anterior regeneration 

 has occured sometiraes in the absence of any at tlie posterior end but 

 posterior ro tlie piece 5 — 7 conditions are reversed; posterior rege- 

 neration is inore rapid and luay occur in tlie absence of anterior re- 

 generation. For the lovel of the 6rh soniite the minimal size is four 

 somites. li — 0. At the next level it is also four somites. 7 — 10. and 

 for tho 8th and last level six somites are roquirod. 



Posterior Regeneration. 



Exjierimonts in posterior regeneration were conduotod with both 

 Lumhrivulus and Limnodriliu^t but since C. MtJXLER. in a recent papor 

 (OS), has covered niuch the same ground I sliall not touch upon thoso 

 experimonts hero oxoopt insofar as the results differ froni thoso ob- 

 tained bv Müller. Upon removing 15 to 60 of the posterior somites 

 in Lumbncuhis and Tuhifej: he found that in the space of 14 days all 

 the Worms had replaced practically the same number of somites 

 vi2. 25. the \-ariation, according to his tables, generally being but 

 1 to 3 somites. Furthermore 25 additional somites were regenerated 

 by the same individuals hi each of three succeeding periods of 14 days. 

 As tlie result of tliese experimencs MtJLLER raaintains that »Die Zahl 

 der neu gebildeten Segmente stellt in gleichem Verhältnis zu Dauer 

 der Regeneration. In gleichen Zeiten werden gleich viel Segmente 

 gebildet «. 



As the foUowing records will show. tho results obtained by nie 

 were not so uniform either in the number of segments regenerated 

 diiring the first pexiod or in maintaining this number during a suc- 

 ceeding pexiod. It should be notod that bofore coiintiiig the regene- 

 rated somites the worms were always anaesthetized to insure accuracy. 



On June 30tli, 190S, ton worms {Lumbrkulus) were each cut into 

 teil pieces of 20 somites each (e. g. 1 — 20. 21 — 40, etc.). All of the 

 pieces were kept separately biit under exactly the same conditions. 

 At the end of two weeks the number of somites regenerated by e^ch 

 piece was counted. The first level, of course, retained the origitiaJ 



