6 General Fart. 



and the halves of the chromosomes, apparently, are (Fig. 3, i) thereby drawn 

 away from each other, so as to form two separate gi-oups (Fig. 3, s). Bach 

 gi'oup is the beginning of a new nucleus, for its chromosomes unite again to 

 form a new network, and a nuclear membrane ai'ises round it (Fig, 3, e). Before 

 this happens, however, the protoplasm begins to divide into two parts cowe- 

 sponding to the new nuclei. 



^ 



(^ 



Fig. 3. Diagram of 

 indirect nuclear division, 

 c centrosome. See text. 

 — Orig. 



Bach cell of the animal body has an entity of its own, but it 

 differs from the Amcsba, in that it is a member of, and to a certain 

 extent subordinate to, a great whole. The degree of its independence 

 varies, however, very considerably. Some cells, called wandering 

 cells, retain throughout life a very considerable freedom, and, 

 in nearly all respects, remain on a level vdth the Amoeba. They 

 have the power of protruding pseudopodia, and each moves about 

 by itself J freely, in the spaces of the body : moreover, whilst most 

 other cells (see the section on the alimentary canal) can only absorb 

 food in a liquid form, the wandering cells can also take up hard 

 particles and dissolve them. Sometimes this peculiarity seems to be 

 exerted even against the organism itself : for instance, in those cases 

 where (as in the metamorphosis of Insects) some organs atrophy — 

 without the death of the creature itself — the vrandering cells eat up 

 the dead parts and digest them. They devour also foreign bodies, 

 such as Bacteria, which have got into the body. The blood 

 corpuscles of most invertebrate animals,* and the white blood 

 corpuscles of the Vertebrata, are wandering cells. There are still 

 other free cells, viz., the red blood corpuscles of Vertebrates, which 



* All the Metazoa, with the exception of the Vertebrata, belong to this group. 



