Heteronemertea 165 



METHOD FOR STUDIES ON REGENERATION 



In nearly all species of nemerteans the body quickly restores a missing 

 posterior extremity. In some forms this ability is limited to the posterior 

 half of the body, but in others the head and a small portion of the foregut 

 region, or even the head alone, without any part of the alimentary canal, 

 can regenerate all the missing parts. Anterior regeneration is usually 

 limited to the head in front of the brain but a few species, particularly 

 those of the genus Lineus, can reproduce the entire body in miniature 

 from any small fragment except the minute piece anterior to the brain. 

 Even a small sector of a fragment, if it contains a tiny piece of the lateral 

 nerve cord, is likewise endowed with the capacity for complete regenera- 

 tion and reorganization. Curiously enough, individuals of some species 

 live longer in captivity with the head removed than with the entire body 

 intact, for the reason that the decapitated body is less restless. 



Operations for regeneration experiments are usually performed with- 

 out the use of an anesthetic, although the head may be removed if neces- 

 sary. The worm is placed in a small pool of cool water upon a beeswax 

 plate having a suitable concavity. Under the binocular dissecting micro- 

 scope the desired cuts may be made with a cutting blade sharply ground 

 from a curved needle. The fragment is then placed in a vessel or vial 

 of clean water. 



In some species the fragments are less restless, and consequently re- 

 generate better, if a few bits of shells or small pebbles or sand grains are 

 placed in the vial or dish. This procedure may sometimes make the 

 difference between the success or failure of the experiment. Food may be 

 supplied after the mouth and digestive tract become functional. 



