THE PHENOMENA OF LIFE. 17 



halves of the chromosomes in such a way that one-half of each is turned 

 toward one pole, and the other half toward the other. As this con- 

 tinues, the two groups, which are equal in size, draw away from each 

 other and from the equator, each group being formed of daughter 

 chromosomes. 



Ketrogressive stage (anapliases and telopliases) . The two groups 

 (daughter chromosomes) now gradually approach their respective poles, 

 or centrosomes, and the equator becomes free. On reaching the pole, 

 each group gathers in a form which is similar in arrangement to the 

 monaster and is known as the diaster. During this time the cell body 

 becomes slightly constricted by a circular groove at its equatorial plane. 

 Soon afterward the fibrils of the achromatic spindle which connect the 

 two groups begin to grow dim and finally disappear. The daughter 

 chromosomes assume the form of threads twisted in a coil and develop 

 each a nuclear membrane and a nucleolus, forming a daughter nucleus. 

 The nuclei enlarge and the nuclear threads assume the appearance of the 

 resting state of the nucleus. Meanwhile, the constriction about the 

 body of the cell has become deeper and deeper until the protoplasm is 

 divided into two equal parts, or daughter cells, each with its daughter 

 nucleus, and the process of karyokinesis is completed. 



Differences between Animals and Plants. 



Having considered at some length the vital properties of protoplasm, 

 as shown in cells of vegetable as well as of animal organisms, we are now 

 in a position to discuss the question of the differences between plants and 

 animals. It might at the outset of our inquiry have seemed an unnec- 

 essary thing to recount the distinctions which exist between an animal 

 and a vegetable as they are in many cases so obvious, but, however great 

 the differences may be between the higher animals and plants, in the 

 lowest of them the distinctions are much less plain. 



In the first place, it is important to lay stress upon the differences 

 between vegetable and animal cells, first as regards their structure and 

 next as regards their functions. 



(L) It has been already mentioned that in animal cells an envelope 

 or cell-wall is by no means always present. In adult vegetable cells, on 

 the other hand, a well-defined cellulose wall is highly characteristic; 

 this, it should be remembered, is non-nitrogenous, and thus differs 

 chemically as well as structurally from the contained protoplasmic 

 mass. 



Moreover, in vegetable cells (fig. 17, B), the protoplasmic contents 

 of the cell fall into two subdivisions: (1) a continuous film which lines 

 the interior of the cellulose wall; and (2) a reticulate mass contain- 



