I. RHIZOPODA 



171 



for taking nourishment. These differ from true appendages in that they 

 are not constant, but are formed according to demand and again disappear. 

 A pseudopodium arises when the protoplasm streams to one point of the 

 body and extends as a process beyond the surface. Since the process 

 becomes attached and draws the body after it, or since the protoplasm of the 

 body may flow into it, a slow change of place occurs. In either case the 

 process disappears in the organism, and new pseudopodia are formed 

 at other places which are retracted in turn. This t^^pe of locomotion is 

 called amoeboid after the Amivba, in which it was first studied. When 

 the Rhizopoda in their wanderings meet particles of nourishment, they 

 enclose them with their protoplasm and take them into the interior of 

 the body (fig. 117, N). 



Fig. 117. 

 Fig. 117. — Amceha proteus (after Lcidy) 

 ectosarc; n, nucleus; A'', food-body. 



Fig. 118. — Rotalia freyeri (from Lang, after M. Schultze). 



Fig. iiS 



ci\ contractile vacuole; en, entosarc; ek^ 



The shape of the pseudopodia is approximately constant for each 

 species, but it varies so with different forms that it may be used not only 

 for separating species but groups. On the one hand, there are finger-like 

 pseudopodia (fig. 117), on the other, those of such delicacy that even 

 under strong magnification they appear like fine threads (fig. 118); and 

 between these extremes many intermediate forms. Thread-like pseudo- 

 podia usually branch, and when the branches meet they may fuse and 

 form anastomoses, from which it follows that the pseudopodia are not 



