THE BIOLOGY OF THE CELL SURFACE 



To Haeckel we owe the application of the term, exoplasm, 

 to the superficial cytoplasm of the Protozoa. Writing in 

 1873 on the morphology of the Infusoria, he emphasized the 

 differentiation of the protoplasmic body into a bright, 

 firmer cortical substance and a granular, softer medullary 

 substance, a differentiation found also in Amoeba as in 

 many parenchyma cells of higher animals. This outer 

 layer is further distinguished from the medullary portion of 

 the cytoplasm through a lower water content and an 

 independent contractility. Later authors, as Biitschli, 

 Doflein and others, have merely reiterated Haeckel's 

 original description, confirming it through their own 

 observations. 



The protozoan ectoplasm may be highly differentiated: 

 for support and protection; for motility; for food-capture; 

 and for oral and anal modifications. In it are located the 

 contractile vacuoles. On the basis of their means of 

 locomotion Protozoa are classified into four groups: those 

 like the Amoeba, that move by means of pseudopodia; 

 those that move by means of flagella; those like Para- 

 moecium that move by means of cilia, and, in a negative 

 way, those like the Sporozoa, to which tl,ie organism that 

 causes malaria belongs, which are characterized at least 

 during one period of their life-history by lack of locomotor- 

 apparatus. In other words, the classification of the groups 

 is built upon ectoplasmic differentiation.^ 



^ Though this book concerns itself with the animal cell, I may note 

 in passing that in many plant cells, especially in the higher, multi- 

 cellular, organisms, the living cytoplasm is entirely superficial in 

 location, the interior of the cell being a vacuole of non-living materials. 

 Also, I may call attention to the Bacteria which possess a strongly 

 marked ectoplasm, investigated especially by Gutstein {ic}26 a7id 

 earlier). The ectoplasm of Bacteria has been much discussed in 

 connection with their structure in relation to the valuable diagnostic 

 aid for identifying these organisms furnished by the Gram stain. 

 (See Schumacher igjS and earlier.) 



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