1921] NATURAL SCIENCES OF PHILADELPHIA. 115 



with sufficient clearness to be able to explain the facts. The pseu- 

 dopodia, at the same time that they retract and shorten, move 

 backward while the central granule is brought forward; this dis- 

 placement of the pseudopodia is, in fact, to be compared to the 

 shutting of an umbrella, whose ribs are brought down and collapse 

 together. As for the cause of the shutting, it must very likely 

 be sought in internal movements inside the plasma, which result 

 in an accumulation of clear pure ectoplasm at the anterior extremity, 

 if we can imagine a current coming from behind and pushing the 

 central granule forward along the longitudinal axis of the body, 

 and at the same time lateral backward currents pushing the axial 

 rods downward, we can get an idea of the transformation. 



As it is, the Flagellate, which now measm-es about 37[x in length, 

 i. e., l\i more than in the Heliozoan shape, immediately takes to 

 swimming, rapidly drawn forward by its flagella. As already noted, 

 some of the pseudopodia, or rather some of the axial threads with 

 their covering of granulations, are very often seen traihng laterally 

 or behind, but I never could see, as Blochmann said of his unidenti- 

 fied Dimorpha, the animalcule swimming with completely and nor- 

 mally expanded pseudopodia. 



Swimming never lasts very long; the most trifling cause is suffi- 

 cient to instigate reversion to the Heliozoan type; the animalcule 

 is seen to stop, and suddenly the pseudopodia make their appear- 

 ance, lengthening at the same tune as they are brought forward, 

 while the central granule moves downward toward the center of 

 the body The same kind of phenomenon has taken place, which 

 we compared to the shutting of an umbrella, but it is now the open- 

 ing, and it has been even more rapid.' This transformation from 

 the Flagellate state to the Heliozoan type is brought about by any- 

 thing that might be supposed to indicate trouble or danger — a 

 small Infusorian in the vicinity, a current of water, etc.- — while 

 the inverse, the transformation from the Heliozoan into a Flagel- 

 late, is much more difficult to produce; a strong light, however, 

 which provokes the displacement of the animalcule toward a cooler 

 region, is often successful. Very probably, the Heliozoan form is 

 the form of defense, the pseudopodia firmly affixing the body to 

 resist currents, and at the same time it is the fishing-form, allowing 

 small organisms to be caught by the pseudopodia. 



3 This reversion is still more shortened by the action of a chemical reagent; 

 in one particular case, for instance, I have seen the transformation entirely 

 effected in the half of a second, under the influence of a verj^ weak current of 

 glycerin and carmine. 



