312 PARASITES OF THE DOMESTIC ANIMALS 



much greater specialization in some than in others. While a nucleus is 

 not easily demonstrable in certain of the Protozoa, most have one or 

 more distinct nuclei, in this, as in other respects, possessing the essential 

 parts of a typical cell. 



Ameba. — A simple representative of the Protozoa is the Ameba 

 (Fig. 168) which may be found in .most any still water, most readily in 

 the ooze ujion the bottom or adhering to leaves or other submerged 



Fig. 168. — -Ameba proteus (after Crawley, from Doflein; Cir. 

 No. 194, Bureau An. Ind., U. S. Dept. Agr.). 



objects. Search of such material under the low power of the microscope 

 will reveal this organism as a minute protoplasmic particle which slowly 

 changes its shape and location by a peculiar flowing and extension of 

 the cytoplasm at one or more points, forming irregular, often finger-like, 

 projections, — the pseudopodia. These may be withdrawn or the whole 

 substance of the animal may appear to flow into one of the projections; 

 by this manner of locomotion it may slowly pass out of the microscopic 

 field. Close study of the organism will reveal two distinct regions, an 

 outer hyaline, — the ectoplasm (ectosarc), and a central more granular 

 and less transparent part, — the endoplasm (endosarc) . Within the latter 

 may be seen the food vacuoles which are rounded or oval, of varying 



