I So 



THE BEHAVIOR OF LOWER ORGANISMS. 



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

 Rhumbler(i89S, 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 (3), at this point, 

 7> 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 Ajnoeba terricola {ver- 

 rucosa^ 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).! 



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 (3, c), separating off the posterior end (rf). 

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



Fig. 63.* 



