226 THE BEHAVIOR OF LOWER ORGANISMS. 



finally resolvable into the action of chemical and physical laws, but we 

 must admit that we have not arrived at this goal even for the simpler 

 activities of Amoeba. 



THE BEHAVIOR OF AMCEBA FROM THE STANDPOINT OF THE 

 COMPARATIVE STUDY OF ANIMAL BEHAVIOR. 



HABITS IN AMOEBA. 



Although in general Amoeba has the rolling movement of a drop of 

 fluid, yet this statement by no means brings out all the characteristics 

 of the movement in any given species of Amoeba. Different kinds of 

 Amoebae move differently, and the differences are in many cases not 

 such as can be accounted for by differences in the state of aggregation 

 of the body substance. Some Amoebae, as is well known, form many 

 pseudopodia, others few or none. Different Amoebae have different 

 characteristic forms in locomotion. But more striking than these gen- 

 erally recognized peculiarities are certain others of a more special char- 

 acter. A creeping Amoeba angulata,a. we have seen above, frequently 

 pushes upward and forward at the anterior end a short, acute pseudo- 

 podium, which waves slightly from side to side like an antenna (p. 177 

 and Fig. 62, c). This peculiar habit is much more pronounced in 

 Amoeba velata Parona, according to Penard (1902). In this animal 

 the free anterior pseudopodium may extend for a length greater than 

 the diameter of the body ; Penard compares it directly to a tentacle. 

 Some other species of Amoeba never send forward such an antenna-like 

 pseudopodium. The great work of Penard (/. c.} contains innumer- 

 able instances of such peculiarities of form, movement, and function 

 among the different species of Amoeba and other Rhizopods ; some of 

 them are collected in that author's interesting section on the pseudo- 

 podia (/. c., pp. 625-629). It is not necessary to take these up in detail 

 here. The point of interest is that different sorts of Amoebae have dif- 

 ferent customary methods of action, such as are commonly spoken of 

 as " habits"* in higher animals, and that these " habits" are no more 

 easily explicable on direct physical grounds in Amoeba than in higher 

 animals. Let anyone attempt, for example, to explain from the 

 physics of viscous fluids why Amoeba velata or A. angulata push 

 out an antenna-like pseudopodium at the anterior end and wave it from 

 side to side, while Amoeba proteus and A. Umax do not. 



* The word habit is, of course, not used here of a method of action acquired 

 during the life of the individual, but merely of a fixed method of behavior. At 

 all events, it is difficult to distinguish between these two things where individual 

 organisms, as in Amoeba, have lived as long as the race. 



