LESSON X 



PARAMOECIUM, STYLONYCHIA, AND OXYTRICHA 



IT will have been noticed with regard to the simple uni- 

 cellular organisms hitherto considered that all are not equally 

 simple : that Protamceba (Fig. 2, p. 9) and Micrococcus 

 (Fig. 1 6, p. 85), may be considered as the lowest of all, 

 and that the others are raised above these forms in the scale 

 of being in virtue of the possession of nucleus or contractile 

 vacuole, or of flagella, or even, as in the case of Euglena 

 (Fig. 5, p. 45), of a mouth and gullet. 



Thus we may speak of any of the organisms already 

 studied as relatively " high " or " low " with regard to the 

 rest : the lowest or least differentiated forms being those 

 which approach most nearly to the simplest conception of a 

 living thing a mere lump of protoplasm : the highest or 

 most differentiated those in which the greatest complication 

 of structure has been attained. It must be remembered, 

 too, that this increase in structural complexity is always 

 accompanied by some degree of division of physiological 

 labour, or, in other words, that morphological and physio- 

 logical differentiation go hand in hand. 



We have now to consider certain organisms in which this 

 differentiation has gone much further ; which have, in fact, 



