8 BRANCH PROTOZOA 



Respiration, or the taking in of oxygen and the giving off 

 of carbonic acid gas and other wastes, is effected by the al)sorb- 

 tion of the one and the throwing off of the other through the 

 surface. 



Excretion takes place through the surface or through the 

 contractile vacuole, there being a definite point at which the 

 waste is ejected in the more advanced forms, such as the 

 Paranurcimn and the Vorticella. 



Multiplication. — While these life processes are going on, the 

 animal grows or increases in size. This size must necessarily 

 be very limited, for only small animals could live in this ]>rimi- 

 tive way; hence, when the protozoan has reached a sufficient 

 size, it divides into two complete halves, each half containing 

 its share of the original cell-nucleus, as well as of the cytoplasm 

 or protoplasmic cell body. This cell division, or the multiplica- 

 tion of individuals, is called fission. After simple fission has 

 taken place for many generations the fusion of two individuals, 

 or conjugation, in which the nucleus of one individual is broken 

 up and fused with that of the other, occurs. After this fusion, 

 the process of fission continues, in which each new individual now 

 contains a portion of the two parent nuclei which were fused 

 in conjugation, instead of one parent nucleus as before con- 

 jugation. This surely contains a suggestion of sexual mul- 

 tiplication, though the conjugating cells may appear exactly 

 alike. However, instances are given in which the individuals 

 differ in size, the " males " being smaller and more mobile. 

 Also we see, not exactly " alternation of generations," Init, at 

 any rate, alternation of methods of reproduction. 



Animal Mind.^ — Of the mental life of the protozoan little is 

 know^n. If the rudiments of future complex animals is fore- 

 shadowed in the protozoan, why may we not recognize the fact 

 that here, too, is found the merest suggestion of the mental life 

 as well? 



It has been abundantly demonstratetl that protozoans possess 

 irritability and contractility. It has been shown that they are 

 sensitive to touch or contact, and, indeed, can discriminate 



1 Mind is here used in the biologic sense, and is the "sum total of all 

 psychic changes, actions, and reactions." — Jordan and Kellogg's " Evolu- 

 tion and Animal Life," p. 448. 



