STRUCTURAL DIFFERENTIATIONS 143 



s 



podia of many Foraminifera and Radiolaria which stand out in all 

 directions from the cell. 



/^iZoj^of/za.— Structurally filopodia are entirely different from the 

 types described above, being formed of clear hyaline ectoplasm in 

 typical cases, or they contain a few granules indicative of endo- 

 plasm (Fig. 10, p. 32). They are usually long and slender and with 

 rounded ends giving the impression of slender glass rods. In some 

 forms there is a tendency to branch at the ends as in Euglypha 

 aheolata (Fig. 8, p. 30), but there is never anastomosis. Some- 

 times they sway back and forth like a filament of Oscillaria, but 

 usually they creep along the substratum where they serve mainly 

 for food capture. 



Filopodia are characteristic of the fresh water testate rhizopods, 

 but are sometimes present in naked types like Amoeba radiosa or 

 Amoeba actinopoda {?). 



Lobopodia.— Lobopodia are made up of granular endoplasm and 

 hyaline ectoplasm, and are temporarily projected portions of the 

 body protoplasm not to be compared with definite locomotor organs 

 of other Protozoa. The inner protoplasm of nearly all kinds of 

 Protozoa with granules of various kinds, food substances more or 

 less digested, and waste materials, is in constant movement called 

 cyclosis. In more highly differentiated forms, and in organisms with 

 a firm cell membrane, this movement is confined to the internal 

 protoplasm and the form of the cell is not affected by it. In the 

 shell-less rhizopods, however, there is no such outer covering, and 

 the peripheral protoplasm gives way at the weakest points, and an 

 outward flow of protoplasm with corresponding change in the form 

 of the body results (see Chapter IV). If such a weak point is con- 

 stant in position, a constant flow in its direction is the outcome, 

 and the Amoeba, consisting of practically one pseudopodium, as in 

 the Umax types, moves in one direction (Fig. 29, p. 67). In 

 Amoeba verrucosa a delicate periplast surrounds a somewhat dense 

 protoplasm which, accumulating on one side (according to Rhumbler 

 1898), causes the cell to roll over. 



Withdrawal of pseudopodia is accomplished by their absorption 

 into the body substance, and is accompanied by a wrinkling of the 

 denser ectoplasm preparatory to its transformation into endoplasm 

 (see Schaeft'er). 



In pseudopodia generally it is evident that we have to do with 

 different types of structure which, in only a few instances, can 

 be regarded as motile organs. Axopodia, with their axial filaments 

 derived from kinetic elements, are closely related to flagella and may 

 be regarded as organs of locomotion, but the other types, which may 

 represent highly modified axopodia, have lost the kinetic elements, 

 if they ever had them, and are useful only as food-catching organs. 

 In most rhizopods the entire organism is the motile element, rhizo- 



