GENERAL BIOLOGY. 16 



remain in this condition for a variable period, reminding us of 

 the similar behavior of Torula. 



Amceba reproduces by fission, in which the nucleus takes a 

 prominent if not a directive part, as seems likely in regard to 

 all the functions of unicellular organisms. 



CDnclnsions. — It is evident that Amoeba is, in much of its 

 behavior, closely related to both colored and colorless one-celled 

 plants. All of the three classes of organisms are composed of 

 protoplasm ; each can. construct protoplasm out of that which 

 is very different from it ; each builds up the inanimate inor- 

 ganic world into itself by virtue of that force which we call 

 vital, but which in its essence we do not understand ; each mul- 

 tiplies by division of itself, and all can only live, move, and 

 have their being under certain definite limitations. But even 

 among forms of life so lowly as those we have been consider- 

 ing, the differences between the animal and vegetable worlds 

 appear. Thus, Amceba never has a cellulose wall, and can not 

 subsist on inorganic food alone. The cellulose wall is not, how- 

 ever, invariably present in plants, though this is generally the 

 case ; and there are animals (Ascidians) with a cellulose invest 

 ment. Such are very exceptional cases. But the law that ani- 

 mals must have organized material {protein) as food is without 

 exception, and forms a broad line of distinction between the 

 animal and vegetable kingdoms. 



Amoeba will receive further consideration later ; in the 

 mean time, we turn to the study of forms of life in many re- 

 spects intermediate between plants and animals, and full of prac- 

 tical interest for mankind, on account of their relations to dis- 

 ease, as revealed by recent investigations. 



PARASITIC ORGANISMS. 



The Fungi. 

 Molds (PenicilKum glaucum and Mucor mucedo). 



Closely related to Torula physiologically, but of more com- 

 plex structure, are the molds, of which we select for convenient 

 study the common green mold (Penicillium), found growing in 

 dark and moist places on bread and similar substances, and the 

 white mold (Mucor), which grows readily on manure. 



The fungi originate in spores, which are essentially like 

 Torula in structure, by a process of budding and longitudinal 

 extension, resulting in the formation of transparent branches 



