Regeneration in Liinibriculus 551 



however, happens very rarely. Lumbriculus also shows a thigmo- 

 tactic reaction. In dishes of water the worms show a tendency to 

 crowd together, rolling up in a ball, at times of considerable size, 

 containing as many as twenty to thirty worms.'' 



Separate pieces taken from different levels also show the same 

 reaction to mechanical stimuli as do the corresponding regions of 

 the normal worm. Only the anterior pieces however come together 

 to form balls. 



AUTOTOMY OR REPRODUCTION 



It is well know that of all the Oligochaeta Lumbriculus possesses 

 the greatest capacity of breaking off pieces of their body when 

 subjected to stimuli. "Wie schon gesagt, sind die Thiere (Lum- 

 briculus) ausserst empfindlich gegen aussere Reize und zerreissen 

 sich haufig schon bei ganz leiser Beriihrung an der getroffenen 



Stelle Deshalb findet man so haufig im freien Wasser, 



noch mehr unter den in GlasgefassengeziichtetenThieren, verstiim- 

 melte Individuen, da sie beim Anstossen an die Wande oder son- 

 stige harte Gegenstande leicht zerbrechen."* 



O. F. Miiller^ also speaks of this behavior. If, he says, Lum- 

 briculi be put into dishes — "so wird man bald an ihnen den 

 Schwanz vermissen; selbst in ihrem natiirlichen Aufenthalt trifft man 

 wenige unbeschadigt an; die meisten sind in Begriff, einen neuen 

 Schwanz, andere einen neuen Kopf, noch andere beides zu ent- 

 wickeln .'.... Demnach scheint dieses Zertheilen ihnen natiirlich 

 zu sein, und vielleicht das Mittel der Erhaltung ihrer Art." 



In Table I, I have summarized Biilow's figures regarding the 

 condition in which the worms are found in nature. These data 

 were obtained from a very large number of individuals. 



From this table we see at a glance how large is the proportion of 

 individuals regenerating, especially those regenerating their tails, 



^ C. M. Child gives a similar description of the behavior of a fresh water nemertean Stichostemma 

 "Several specimens in a jar of clear water will often aggregate in a single mass, crawling over and 

 between each other and finally becoming nearly quiet.'' The Habits and Natural History of Sticho- 

 stemma, Amer. Natur., xxxv, 1901. 



^ O. Diflenbach: Anatomische und systematische Studien au Oligochaetae limicolae. 24 Ber. Ober- 

 hass. Ges., Giessen, 1886. 



' O. F. Miiller: Von Wiirmern des siissen und salzigen Wassers, Kopenhagen, 1771. 



