NATURE OF CELLS 13 



if the cytoplasm is confined to tlie streams noted, it does 

 not completely fill the cell. The spaces between the 

 streams are filled with a watery fluid known as sap, or 

 more properly as cell sap. We must not get the idea from 

 this hair cell that all plant cells have walls about them, for 

 they do not. Certain low plants consist, most of their 

 lives, of a mass of free, nucleated protoplasm not con- 

 fined by walls, but creeping about under decaying logs, 

 leaves, etc. 



Animal cell. — It is rather difficult to find an animal cell 

 in which we can see the protoplasm as plainly as in the 

 melon hair, with- 

 out spending con- X^ -' 



siderable time and L '-is^rfaw- 



labor in staimng, ,^,^ ** J^V J^" 



sectioning, etc. i^i^"!^ ' kj-^^ir- n' 



But the amoeba, a *''^ Z f fl« 1 J? 



very simple animal ' ^^^^^-i \'v4 — /^ 



found in the mud ^ * ^^J J 



and ooze of ponds / ,.' s^. ^^^ 



and ditches, affords ,^-'_' ##*''" * - ,, pci 



an example of an pS 



animal cell that I"iG' 4. — Amoeba, enlarged; cw, contractile vacu- 

 Can be easilv ex- °^® ' ^"' ^°°^ vacuole ; n, nucleus ; ps, pseudo- 

 •^ podia; end, endoplasm; erf, ectoplasm. 



amined. It is so 



small and simple that one cell forms the whole animal, 

 and hence, a study of the amoeba (Fig. 4) constitutes a 

 study of an animal cell. 



Where the amoeba is found. — Living in the ooze and 

 slime on the leaves and sticks in ponds, ditches, and streams, 

 are found many kinds of microscopic animals. It is in 

 such situations and in such company that the amoeba is 



