MOVEMENT AND RESPONSE IN DIFFLUGIA WITH SPECIAL REFERENCE TO THE NATURE OF CYTOPLASMIC CONTRACTION

¹ THE JOHNS HOPKINS UNIVERSITY

1. The fleshy part of Difflugia pyriformis and Difflugia acuminata is in structure much like Amba proteus. There is a thin elastic surface membrane (plasmalemma), a central fluid mass (plasmasol), containing a large granular nucleus, and a relatively solid layer (plasmagel) which surrounds the plasmasol. Probably there is also a hyaline fluid layer between the plasmagel and the plasmalemma but this, if it is present. is much thinner and less conspicuous than in Amba.

2. Locomotion in Difflugia is normally brought about by the extension of pseudopods, one after another, and attachment to the substratum at the tip, followed by contraction which pulls the shell containing the body forward. Movement is consequently intermittent.

3. The elastic strength of the plasmagel is lowest at the tip of the pseudopods. This results in contraction of the plasmagel elsewhere, and this contraction forces the plasmasol out through the plasmagel tube, causing expansion at the tip of the pseudopod. The plasmasol which is in contact with the distal edge of the plasmagel tube continuously gelates and this results in extension of the tube.

4. After the tip of the pseudopod becomes attached, the plasmasol in the tip gelates and the plasmagel throughout the entire pseudopod thickens greatly owing to gelation of adjoining plasmasol. This increases the elastic strength of the plasmagel in the entire pseudopod until it becomes greater here than elsewhere, after which it contracts and the pseudopod becomes shorter and thicker and the plasmasol in it is forced back into the body of the organism.

5. The extension of pseudopods in Difflugia is in principle the same as in Amba proteus, and contraction is probably also the same in principle, but it is much more pronounced and much more highly specialized in Difflugia than in Amba, in which it does not function appreciably in the process of locomotion.

6. The pseudopods in Difflugia after they are extended wave about considerably. This is doubtless due to unequal local contraction of the plasmagel on opposite sides.

7. If the shell of Difflugia pyriformis is broken, it leaves the shell in the course of a day or so and moves about fairly freely. Specimens out of the shell sometimes live for a week or more under a cover-glass supported and sealed with a ridge of vaseline. After they have been out of the shell for some time the process of locomotion in such specimens is in all respects like that in Amba, although it is usually much more irregular in direction. Contraction of extended pseudopods, so conspicuous in the process of locomotion in specimens containing shells, has practically disappeared.

8. Difflugia pyriformis aggregates on the more illuminated side of dishes in moderate illumination. It does not orient precisely. It is less active in high illumination than in low, especially when it is out of the shell. It may be that this functions in the aggregation observed. Rapid increase in illumination probably causes decrease in the rate of streaming. but this, if it occurs, is much less marked than it is in Amba proteus.

9. Weak local contact stimulation of an extended pseudopod causes sharp bending in this region toward the side stimulated. Strong general contact stimulation causes rapid contraction of the entire pseudopod. The bending is due to local thickening of the plasmagel in the region stimulated. Contraction of the entire pseudopod is due to thickening of the plasmagel in the entire pseudopod.

10. Contact stimulation results, under certain conditions, in gelation which extends far beyond the region stimulated. There is therefore in Difflugia transmission of something akin to an impulse in higher forms.