44 THE ANIMALS AND MAN 



down, becomes attached by its basal end, loses its basal 

 cilia and develops a stalk. 



"Conjugation occurs sometimes, but it is unlike the con- 

 jugation of Paramecium in two important points: Firstly, 

 the conjugation is between two dissimilar forms; an ordi- 

 nary large-stalked form, and a much smaller free-swimming 

 form which has originated by repeated division of a large 

 form. Secondly, the union of the two is a complete 

 and permanent fusion, the smaller being absorbed into 

 the larger. This permanent fusion of a small active 

 cell with a relatively large fixed cell, followed by divis- 

 ion of the fused mass, presents a striking analogy to 

 the process of sexual reproduction occurring in higher 

 animals." • 



The single-celled body. — The study of Amoeba, Para- 

 mecium and Vorticella has made us acquainted with a type of 

 animal body very different from that of the toad or the cray- 

 fish. These extraordinarily minute animals have a body so 

 simple in its composition, compared with the toad's, that if 

 the toad's body be taken for the type of the animal body, 

 Amcsba might readily be thought not to be an animal at all. 

 The body of Amosba is not composed of organs, each wjth a 

 particular function or work to perform. Whatever an Amosba 

 does is done, we may say, with its whole body. But as we 

 learn the things that this formless viscid speck of matter 

 does, we see that it is truly an animal; that it really does 

 those things which we have learned are the necessary life- 

 processes of an animal. Amwba takes up and digests food 

 composed of organic particles; it has the power of motion; 

 it knows when its body comes in contact with some external 

 object, that is, it can feel or has the power of sensation. 

 Amceba takes in oxygen and gives out carbon dioxide, and 

 it can produce new individuals like itself, that is, it has the 

 power of reproduction. But for the performance of these 

 various life-processes or functions it has no widely differing 



