CERTAIN GENERAL CHARACTERISTICS 47 



anteriorly from levels posterior to the cephalic ganglia but does regenerate 

 posterior parts at all levels from a short distance posterior to the ganglia 

 to the posterior end of the body (Child, igo^b). Both rate of growth and 

 total length of posterior new tissue produced in pieces kept without food 

 decrease from anterior to posterior levels. Rates and amounts of regen- 

 eration are considerably greater at any level when the cephalic ganglia 

 are present than when they are absent. Pieces without ganglia are in- 

 capable of normal co-ordinated locomotion and show little motor activ- 

 ity. Apparently growth of the posterior regenerating tissue is stimulated 

 in the normally active animal. Various rhabdocoel species show essen- 

 tially similar conditions. 



DATA FROM OTHER GROUPS 



Some species of nemerteans show even greater capacity for reconstitu- 

 tion than planarians. According to Nusbaum and Oxner (191 1), the 

 slender form of Linens ruber reconstitutes complete individuals at all 

 levels; but pieces from the middle region have the highest rate. More 

 recently Coe (193 1) has found in L. vegetus and L. socialis in general a 

 decrease in rate from anterior to posterior levels, but with considerable 

 variation. 



The many studies of regeneration in the annelids show very different 

 degrees of regenerative capacity in different species. Briefly stated, the 

 relation between regeneration and body-level in polychetes and oligo- 

 chetes is, in general, as follows: In many forms studied the rate of 

 regeneration at different levels has not been determined; but, according 

 to the data at hand, rate of head regeneration, and in many species ability 

 to regenerate a head, decrease from anterior to posterior levels. In some 

 species a head is regenerated only at extreme anterior levels. Ability to 

 regenerate a posterior end usually increases from extreme anterior levels 

 over a certain portion of body length, which is very different in different 

 species; and at more posterior levels rate of posterior regeneration de- 

 creases. In short, the differences in rate of regeneration at different body- 

 levels in those forms which are capable of regeneration over most of the 

 body length do not differ very greatly from those in planarians; but 

 capacity for, and rate of, posterior regeneration usually increase over a 

 greater distance from the anterior end than in planarians, though not 

 necessarily greater in proportion to body length. ^^ 



'■•See Hescheler, 1896; Morgan, 1897; Morgulis, 1907, 1909; H. R. Hunt, 1915; Hyman, 

 1916a; Korschelt, 1919; Sayles, 1934; and references cited by these authors. See also Sayles, 

 1940, Biol. Bull., 78, 3. 



