A STUDY OF METAMERISM. 445 



these 110 individuals, there results the general rule that the 

 bands occur upon the third and fourth somites, then upon 

 every other or alternate one up to and including the twelfth, 

 then (in the region of the bud) upon every fourth one up to 

 and including the twenty-fifth, then upon every fifth one up 

 to and including the forty-first, after which the exceptions 

 become so numerous that no rule is evident. The examina- 

 tion of so many cases shows a definite tendency to limitation 

 in the bands to certain somites in the anterior region, and a 

 greater and greater irregularity in the posterior region." 

 After illustrating some cases of failure in the normal 

 arrangement of the bands, Andrews adds, " These facts seem 

 sufficient to indicate that we have in this Syllid a marked 

 tendency to the acquirement of a regular metameric marking, 

 which, however, does not coincide with the raetamerisation of 

 the somites, but tends to follow a special law best expressed 

 in the oldest part of the body in which certain alternating 

 coloured and not coloured somites are distinguishable — a series 

 of groups or combinations of somites thus following one 

 another." 



It is not without importance to find in the typically meta- 

 meric Annelids regular serial markings following definite laws 

 in each portion of the body. Groups of metameres seem 

 here to act as a unit. This case is certainly paralleled by the 

 colour-bands on the arms of the brittle-stars. The serial 

 repetition of the appendages of the Crustacea furnish examples 

 of somewhat similar regional variation. It is not improbable 

 that if we find an explanation for one set of phenomena we 

 will be able to explain them all. 



XII. Regeneration in Earthworms. 

 In the winter of 1887-8 I made a small number of experi- 

 ments to determine the extent of regeneration in the earth- 

 worm. Again, in the spring of 1892, another series of 

 experiments were started, but an accident spoiled the results. 

 In the past winter of 1893-41 made a more elaborate and sys- 

 tematic attempt to work out the same problem. 1 am much 



