Chemistry of Living Matter and Cell Division 99 



somes have gathered at the equatorial plane and are then separating. 

 All the other phases cover a much longer period, and as they pass 

 through various stages, are therefore used in the plural. 



In different types of cells, all of these stages vary a little as to length 

 of time and as to the method in which and by which particular cen- 

 trosomes, skeins (also called spiremes), spindles, and chromosomes, 

 arrange themselves. It is well to note that in the higher forms of 

 plants, centrosomes have not been seen, and that there is a difference 

 between plants and animals in the way the cytoplasm divides. In the 

 animal cells, as shown in the drawing, the cell walls indent until the 

 two indented portions meet, and the separation takes place in that way; 

 whereas, in the plant cell the cell-wall does not indent, but the wall 

 becomes thicker and thicker until a definite cell-wall has been grown 

 for the two new cells. 



There are exceptions as to just when and how the spindle forms. 

 In some species of salamander, the spindle begins outside of the nucleus, 

 and then, as the nuclear membrane disappears, the fibers pass through 

 the nucleus itself. 



THE REAL MEANING OF MITOSIS 



The real significance of mitosis is found in the fact that the chromo- 

 somes (a more detailed study of which will be taken up as soon as the 

 protozoa have been studied) split in two lengthwise and that the chromo- 

 somes are practically the only known visible carriers of characteristics 

 that pass from a parent cell to become a new individual. Whatever an 

 offspring is to obtain from its parents must, therefore, be already present 

 in the chromosomes of the various germ cells of the parents, or it cannot 

 be inherited by the offspring. 



A little later it will be explained how the lengthwise dividing of the 

 chromosome means that each new individual obtains one-half its chro- 

 matin matter from each parent. As the chromosomes carry the factors 

 which produce the various characteristics each individual possesses, it 

 follows that each new individual receives one-half of his various charac- 

 teristics from the father and one-half from its mother, although 

 usually these are not evenly distributed as to quantity, and possibly, 

 quality. For example, we may, so far as external appearance go, resem- 

 ble our fathers, yet have our mother's mental characteristics. One must, 

 therefore, not confuse the characteristics which can be seen and are very 

 conspicuous, with those which may not be seen, but which may never- 

 theless be much more important. 



By remembering this statement one may understand the biologist's 

 division of all cells in the body into two great groups. These two 

 groups are known as somatoplasm ( ) and germplasm 



( ). The latter consists of those particular cells 



which will reproduce offspring like the parent, while the somatoplasm 

 consists of all the other cells of the body. It can be imagined from 



