The Biological Record 323 



be separated into two principal parts, one known as the 

 cytoplasm, which is the bulk of the cell, and the other the 

 nucleus, which is a more specialized portion lying within 

 the other. There is also an internal center or focus faintly 

 distinguishable, called the centrosome, and the whole is 

 enclosed in a sort of wall or skin. Such is a typical cell. 

 There are many which this description does not cover 

 because of variable and abnormal conditions, but this 

 illustrates the general type. 



All living bodies are cells or are built up of cells. The 

 invisible microbe of one cell only, and the human being 

 of uncountable millions and the whole scale of living crea- 

 tion is thus constructed. The growth may, however ap- 

 propriate the aid of nonliving secreted structure, such as 

 shells and frames of indurated matters, which in a certain 

 sense are not living although produced and maintained by 

 hfe. 



The process by which an animal or plant grows, is simply 

 by the continued subdivision of the cells of its substance, 

 each of which enlarges to a certain ripeness, and then divides 

 into two, each of which continues to enlarge and divide until 

 its destiny is fulfilled. This fulfillment of destiny varies 

 greatly. It may be that a specialized cell such as one bud- 

 ding in the skin growth of an animal, is pushed into external 

 wear and injury, and is destined merely to resist for a time 

 and die sterile, and fall away, to give place to the new 

 which a nearby parent cell emits in continuing fertility, 

 until old age ends its powers. On the other hand some 

 cells thus dividing in growth, and preserved in the securest 

 recesses of the body, are endowed with all the heredity of 



