12 LIBBIE H. HYMAN AND ALBERT E. GALIGHER 



the experiments the posterior pieces consume more oxygen than 

 the middle pieces and in the majority of cases they also consmne 

 more than the anterior pieces. In experiment 13 the oxygen 

 consumption of the posterior pieces is the same as that of the 

 anterior pieces, while in experiment 2 it is but slightly larger 

 than the latter; but in most cases the posterior pieces have a 

 markedly higher rate of respiration than the other pieces. 

 The differences in the oxygen consumption in different experi- 

 ments may be assigned to variations in the animals themselves. 

 The results on the oxygen consumption at different levels are 

 therefore in complete accord with the susceptibility gradients, 

 as shown in figure 1. The existence of metabolic gradient in 

 this annelid may be regarded as demonstrated. 



EXPERIMENTS ON NEREIS 



1. The susceptibility gradient of polychaetes. Owing to the 

 opacity and toughness of the majority of polychaetes, it has 

 not been possible to apply the susceptibility method to them 

 except in the case of the family SyUidae. In this family the 

 worms are of small size and sufficiently delicate aud transpar- 

 ent to permit observations on the death gradient. In the Syllid 

 Autolytus cornutus the senior author found the gradient to be 

 like that already described for oHgochaetes (Hyman, '16, p. 118). 

 There are further at hand the observations of Cwikhtzer, ('05) on 

 the death gradient of Ophyotrocha puerilis, one of the Eunicidae. 

 Ill order to study the regenerative capacity of this species, Cwik- 

 htzer cut off very small portions of the head and lioted in many 

 of the operated individuals the occurrence of disintegration proc- 

 esses. These changes began first at the posterior end, then at 

 the head, or at both anterior and posterior ends simultaneously, 

 and proceeded from both ends toward the middle. In Nereis 

 kept in the laboratory the senior author has noted in several 

 cases the death of the posterior region, beginning at the anal 

 segment and proceeding forward. These scattered observa- 

 tions indicate that the susceptibility gradient of polychaetes is 

 similar to that of the oligochaetes. 



