^ 86 Erste Sektion: Cytologie und Protozoenkunde. Erste Sitzung. 



physical and chemical needs; and thus giving the cell a power 

 of resistance to new factors introduced or new forces impin- 

 ding upon it. In its final analysis, is not this resistance that 

 which maintains the species; and, in fact, that which we call 

 heredity ? 



This resistance seems to remain so long as protoplasm re- 

 mains uncoagulated. It ceases when coagulation sets in. The 

 application of an acid, for instance, may so violently disturb the 

 existing adjustment of various currents of forces, as to forever 

 prevent their resuming the original balance, in which case the 

 protoplasm is killed. 



Development of Structure and Polarity. If 

 we compare Amoeba proteus with Amoeba verrucosa, fig. i, pl. Ia, 

 Amoeba villosa, fig. 2, Aredia diseoides, fig. 3, and the Walking cell, 

 fig. 4, pl. Ib, we may observe an evolution of structure of a more 

 or less permanent type. As compared with Amoeba proteus, for 

 instance, the granules in Amoeba verrucosa flow more regularly in 

 restricted paths. If we attempt to explain the pseudopodia in 

 Amoeba proteus, by the assumption of Variation in surface tension, 

 then we are confronted with the question why those variations 

 do not oeeur also in Amoeba verrucosa and in Amoeba villosa, li- 

 ving as they do in the same water, under precisely similar con- 

 ditions. We avoid this difficulty if we assume that the formation 

 of pseudopodia is due to unequal contraction of the cytoplasm 

 in different parts of the cell. With an uncoordinated protoplasmic 

 contraction, pseudopodia will oeeur on any point of the body; 

 while with a definite coordination of protoplasmic contractions, a 

 definite direction must also be given to the flow of the proto- 

 plasmic granules. 



It is conceivable that this definite flow of the protoplasmic 

 granules leads finally to a definite linear arrangement of the par- 

 ticles of which the protoplasm consists. 



Accompanied by a corresponding thikening of the ectosarc, 

 which such repeated lateral contraction may in some way pro- 

 mote, the cell gradually acquires a definite external form, which 

 reveals the polar differentiation already described. External evi- 

 dences of polarity become marked in proportion to the develop- 

 ment, within, of a perfect sequence between those primordial 

 activities called irritability and contractility. The one property 

 makes the cell aware, so to speak, of external influences; the 

 other enables it to seek or avoid the influence and consequently 

 to preserve its own integrity. 



Both irritability and contractility are probably due to a re- 

 gulär sequence in the transformation and transmission of energy; 

 and it is conceivable that out of an uncoordinated transformation 

 and transmission of energy, a regulär sequence may be established 



