416 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



brachial. The articular facets of the nonmusculiir articulations are especially 

 fitted for regeneration only because they are especially adapted for autotomy. 



On December 15 Keichensperger removed all the cirri from eight specimens; 

 on January 17 the first signs of regeneration were visible; on February 20 three 

 showed large regenerating buds, and two additional had buds still further ad- 

 vanced ; on March 7 from five to seven cirri on each animal had attained about one- 

 third of the normal size. The remaining three animals, though still living, showed 

 no trace of regeneration on March 7. 



Regeneration of the cirri, though it occurs, proceeds with extreme slowness. 



Keichensperger met with only 11 cases of partial regeneration of the cirri in 

 Antedon mediterranea. Minckert records one in Tropiometra picta, and P. H. 

 Carpenter one in Tropiometra carinata {'i.picta). 



In 2 of tlie 11 cases noticed by Keichensperger, regeneration took place after 

 fracture from natural causes, once from the third and once from the seventh seg- 

 ment. In the other 9 the fracture was artificial, and in these 8 regenerated from 

 the end of an ossicle, and 1 from a cut through the middle. About 170 cirri were 

 used in the experiments, but most of the stumps were cast off by autotomy. 



INFLUENCE OF DIFFERENT FACTORS ON REGENERATION. 



Keichensperger confirms previous investigators when he says that the more 

 unimportant the lost parts are the slower, in general, is the regeneration; the 

 larger the jDortion removed the quicker and stronger will regeneration set in. 



So far as it is possible to estimate, a regenerating arm with a IBr^ as a base 

 grows about twice as rapidly as one arising from one of the distal brachials. 



If on one animal all the arms are cut away at about the tenth brachial, and 

 on another animal of equal vigor only one or two, in general the regenerating 

 buds on the animal deprived of all its arms will reach a length of 0.7 mm. to 

 0.8 mm. when those on the other are at the most 0.4 mm. or 0.5 mm. long. 



During a stay of over five months' duration at Naples Keichensperger was 

 not able to determine any exhaustion of the powers of regeneration in the arms 

 of Antedon mediterranea. 



In three vigorous animals he broke off individual arms at the syzygy between 

 the third and fourth brachials, at intervals of from 8 to 10 days. They always 

 regenerated with almost equal perfection and speed. In two cases the experiment 

 was carried out 12 times on the same animal, and in one case 14 times. There is 

 no difficulty in inducing regenerating buds of the second, third, and even fourth 

 order in any location. 



The assimilation of food can play only a slight part in influencing regener- 

 ative processes. There is practically no diffei'ence in the rapidity of the regener- 

 ation between animals with and without disks. Specimens which are in process 

 of regenerating extensive portions of the arms rarely show the Aasceral mass 

 extended with food; in fact, it is shown by sections through the visceral mass 

 of rapidly regenerating animals that the alimentary tract is almost always empty. 



