THE BEHAVIOR OF LOWER ORGANISMS. 



sufficiently viscous the entire mass of endosarc would be withdrawn, 

 and the pseudopodium would collapse. 



There are certain facts that speak against this second view. Thus, 

 the endosarc often passes out when there is no current away from the 

 mouth of the pseudopodium, so that there can be nothing pulling upon 

 the endosarc. A pseudopodium may be withdrawn when the animal 

 is otherwise quiet ; or, when the animal is stimulated strongly, all the 

 pseudopodia may be withdrawn at the same time, while there is no 

 endosarcal current in the body of the animal. A striking case that 

 belongs here is sometimes to be observed in Amoeba radiosa. This 

 animal frequently floats in the water, with many long, pointed pseudopo- 

 dia radiating in all directions from the body. Now, if the pseudopodia 



are stimulated with a rod, 

 they begin to contract. The 

 endosarc first passes inward, 

 but the resistance of the body 

 is so great that the fluid stops 

 at the base of the pseudo- 

 podia. These, therefore, 

 swell up in a bulbous 

 fashion, as illustrated in 

 Fig. 50. Such cases, indeed 

 all the numerous cases in 

 which the endosarc passes 

 out of a pseudopodium and 

 comes to rest as soon as it has 

 left the latter, can only be ex- 

 plained on the assumption 

 that the endosarc is forced 



out by the contraction of the ectosarc, or by some active movements of 

 the endosarc itself, of a character not understood. 



Further, there are certain facts which speak positively in favor of 

 the view that the production of the wrinkles is due to a contraction of the 

 inner layer of the ectosarc. Thus, when an Amoeba is strongly stimu- 

 lated and withdraws all its pseudopodia quickly, the whole surface of 

 the body becomes rough and wrinkled. The endosarc has not passed 

 out of it, so that it cannot be considered in a state of collapse ; on the con- 

 trary, it is clearly contracted as strongly as possible. Again, if a large 

 pseudopodium is cut from the body, it contracts strongly, showing the 

 rough, wrinkled contour, though the endosarc has not passed out of it. 



FIG. 50.* 



*FiG. 50. Specimen of Amoeba radiosa in which the endosarc has passed out 

 of the distal portions of the pseudopodia into the basal parts, causing them to 

 swell up in a bulbous fashion. 



