THE AXIAL GRADIENTS IN HYDROZOA. 



355 



differences in the stem of Tubularia." Such statements as these 

 display an unpardonable ignorance of the literature dealing 

 with the regeneration of Tubularia, This form has been in- 

 vestigated by a number of well-known zoologists, and twenty 

 years ago the regional differences which Banus denies were 

 demonstrated to exist. 



The first experiments on the regeneration of Tubularia were 

 those of Loeb ('91 and '92), performed at Naples. In the first 

 of these publications (on p. 15) he states that he took very long 

 stems, cut off the roots and polyps, and then divided the remain- 

 ing portion in half. No difference w r as observed in the rate of 

 regeneration of the oral hydranths on the apical and basal pieces. 



FIG. i. Diagram of Tubularia to illustrate method of cutting apical and basa 

 pieces of the stem of equal length; employed in experiments recorded in Tables 

 III., IV., V., VII., IX., and X. a, apical; b, basal. 



The following year he repeated the experiment and this time he 

 observed that in one experiment (he does not state how many 

 experiments were performed) the oral hydranths emerged about 

 twenty-four hours earlier on the apical than on the basal pieces. 

 Owing to the meager details which are furnished regarding these 

 experiments, it is impossible to determine why the same investi- 

 gator working on the same material should at one time obtain 



