AXIAL GRADIENT IN CILIATE INFUSORIA. 37 



present will be scarcely or not at all apparent. If on the other 

 hand the concentration is too low, the results may be complicated 

 by acclimation, the individuals or regions of highest rate showing 

 in general the greatest capacity for acclimation. The proper 

 concentrations for each species must of course be determined by 



experiment. 



II. HETEROTRICHA. 



The species Stentor cceruleus has been the chief experimental 

 material from this group. In KCX the animals do not become 

 elongated and attach themselves but contract to a rounded form 

 and swim continuously backward by means of the cilia. In 

 KCN 0.002 m. at a water-temperature of 25-26 C. all animals 

 (several hundred in each experiment) remain alive and intact 

 and swim continuously during the first hour. At the end of this 

 time a very few individuals show the first stages of disintegration. 

 From this time on death and disintegration occur until at the 

 end of the second hour all are dead. At lower temperatures the 

 survival time is longer. 



The usual course of death and disintegration is indicated in 

 Figs. 1-5. In each figure the disintegrated portion is indicated 

 merely by a dotted outline. While the animal is swimming 

 about the peristome region or some part of it, often a region near 

 the mouth first, begins to swell and bulge. This change spreads 

 over the whole peristome within a few seconds or in many 

 individuals is practically simultaneous in all regions of the 

 peristome (Fig. i). This change is accompanied by complete 

 disappearance of the ectoplasmic striations and other structure in 

 the region involved and the entoplasm slowly swells and spreads 

 out. Within t\vo or three seconds after the first indications of 

 change a halo of blue pigment appears in the water about the 

 disintegrated region which has now lost most of its blue color. 

 After a short pause varying in length in different individuals 

 from twenty or thirty seconds to two or three minutes the disin- 

 tegration extends beyond the peristomal cilia and begins its 

 course toward the aboral end of the body (Fig. 2), obliterating 

 the morphological structure of the cytoplasm as it proceeds. 

 The boundary between the disintegrated and intact region is 

 always sharp and clear and the course of disintegration can be 



