i So 



THE BEHAVIOR OF LOWER ORGANISMS. 



a 



These movements remind one of the " rolling motion" described by 

 Rhumbler(i898, p. 115) for these species, though they take place with- 

 out any noticeable change of form and in a manner entirely different 

 from the movements described by Rhumbler. As we have seen above 

 (p. 140), the normal locomotion of these species is, in a certain sense, 

 of a " rolling" character, so that the phenomena described by Rhumb- 

 ler as the rolling movements, perhaps really presented nothing different 

 in principle from the usual motion, though occurring in a different way 

 because the organism was unattached. 



In addition to movements of the character above described, certain 

 other phenomena show in a different way the contractility of the ecto- 

 sarc. Thus, I stimulated sharply with a glass rod one side of an elon- 

 gated moving specimen of Amoeba 

 Umax about one-third its length from 

 the posterior end (Fig. 63, a}. The 

 body at once contracted rapidly, in a 

 ring-like manner (), at this point, 

 and in about i seconds the posterior 

 portion was cut off completely, save 

 by a fine thread (c), by which it 

 hung to the anterior portion for a 

 minute or two. Later this broke, 

 and the posterior piece finally under- 

 went degeneration. 



Penard, in his great work on the 

 Rhizopoda, describes similar phe- 

 nomena in Amoeba terricola (ver- 

 rttcosa) after injury to the ectosarc. 

 After a small injury the injured region is invaginated, forming a small 

 tube passing inward, which is later resorbed. But if the injury is large 

 the part surrounding it contracts strongly, forming a deep constriction 

 between it and the remainder of the body (Fig. 64), and this injured 

 portion is finally constricted off completely (Penard, 1902, p. 109). f 



Altogether, then, we may consider it thoroughly demonstrated that 

 the ectosarc has the power of contracting in definitely limited regions 

 in such a way as (i) to produce movements of entire pseudopodia com- 

 parable to those of flagella ; (2) to produce ringlike contractions which 

 may even progress so far as to cut the body in two completely. 



We need not, therefore, hesitate to admit the existence of contrac- 

 tions of the ectosarc in ordinary locomotion ; these are, for the rest, 

 as clearly observed as those just described. 



* FIG. 63. An A. Umax is stimulated strongly near the posterior end at a ; the 

 stimulated part thereupon constricts (b, c), separating off the posterior end (rf). 

 tFor other observations on reactions to injuries see pp. 202-204. 



FIG. 63.* 



