28 



NORMAL HISTOLOCY 



whole organism of a diversity in its parts is, therefore, unquestion- 

 able, and the higher we go in the animal kingdom, the greater we 

 find the development of this diversity, coupled with a more and 

 more perfectly adjusted co-operative interdependence of the differ- 

 ent parts of the body. 



In the protozoa the single cell does all the work of the whole 

 organism. In the multicellular animals, the metazoa, this work is 

 distributed among the component cells of the body, each of which 

 has developed an efficiency for performing its special work that 

 would be incompatible with a wider range of duties. 



It is quite impossible to find in nature any example of a cell 

 devoid of all individual peculiarities attributable to differentiation 

 or specialization. We must, therefore, study several varieties of 



Fig. 6. 



Ama-ba pellucida. (Frenzel.) a, ectoplasm; b, endoplasm ; c, nucleus : '', nucleolus ; e, large- 

 contractile v f, incorporated foreign body; g,g, pseudopodia. (It is impossible in 



a line-drawing to reproduce the great translucency of the hyaloplasm and the smaller 

 pseudopodia. The outlines of the latter are so faint that it frequently requires close 

 attention to detect them.) 



cell in order to gain an ideal conception of such a cell. This accom- 

 plished, we may consider those cells which occur in nature as special 

 modifications of thai type. 



Perhaps the simplest cell leading an independent existence is the 

 protozoon, amoeba (Fig. 6). There are several species of amcebse 

 which differ in their morphology, showing that even these simple 

 organisms display considerable differences in structure. These ani- 

 mals are widely distributed in moist earth, upon the surfaces of 

 aquatic plants, and in the soil at the margins of ponds and sluggish, 

 stream-. 



