60 Elementary Biology. 



exemplified the union of a number of amoeboid units after 

 they have to a certain extent exhausted their store of energy 

 by active motion. Evidence produced of late years tends 

 to show that plasmodium formation, or the union of sepa- 

 rate amoeboid units, in other forms as well as in this, is an 

 act intimately connected with reproduction. As explained 

 above (p. 52), sexual reproduction consists in the union of 

 a male with a female cell, followed by the development of 

 the product of union into a new organism or organisms. 

 Here we have union, not of two dissimilar cells, but of many 

 more or less similar cells. Nevertheless there is evidence 

 to show that the union, if it be not truly sexual in its nature, is, 

 so far as we know at present, at least accompanied by several 

 of the phenomena which characterise sexual union of cells. 

 In other words, in the conjugation of the separate amoeboid 

 stages of this simple form we have probably the first appear- 

 ance of sexual union in living things. 



We have seen that the plasmodial stage is sooner or 

 later followed by an encysted or resting- stage, where the 

 protoplasm contracts into a spherical mass, and becomes 

 clothed by a capsule. In the period during which the 

 protoplasm remains encysted, probably certain constructive 

 molecular rearrangements are taking place in the proto- 

 plasm, which result in the revivifying or rejuvenescence of 

 the mass, the energy of the various amoeboid units originally 

 entering into the formation of the plasmodium being, so to 

 speak, concentrated. What meaning must we attach to the 

 cyst? During active amoeboid life carbonic acid and 

 water were being abundantly excreted, as already explained. 

 During the encysted stage, of course, the organism is 

 still living, only the vital phenomena are not so actively 

 manifested. There must, therefore, be a certain quantity 

 of carbonic acid and water produced even then. What be- 

 comes of the excreta ? During the active amoeboid stage, 

 owing to the constant motion and change of position 

 of the different parts of the organism, the excreta escape 



