Evolution 



distribution of the life activities proceed at the same time, until 

 we reach the condition prevailing in the higher animals, where the 

 degree of specialisation almost passes conception. In such there 



is, to begin with, a vast frontier army of skin 

 cells, occupied in securing peace, as far as 

 possible, for the industries that go on within. 

 There are directors and controllers of these 

 industries — the brain cells — with a myriad of 

 workers under their guidance, and a great and 

 complex telegraph system between. The 

 workers themselves are of all descriptions — 

 common labourers like the cells of the muscles; 

 transport workers like those of the circulatory 

 system ; skilled factory hands like those of 

 FiG.26.-Spondyiomorum, a ^]^g Hauds ] cvcu scavcugcrs in the shape of 



small colony of flagellates. o ' o x 



the sweat gland and kidney cells. Nay, 

 there is even a numerous police force, of white blood corpuscles^ 

 which patrol everywhere, arresting intruders and disposing of 

 them by the summary method of swallowing them w^hole. 



Our information regarding the early 

 history of this co-operative movement 

 is fragmentary and incomplete, for 

 only an odd species or so seems to 

 survive of the group which we regard 

 as the earliest of multicellular animals. 

 In certain forms which are still essen- 

 tially unicellular, such as the Spondy- 

 lomorum shown in Fig. 26, there is a 

 tendency to form smaller or larger cell 

 colonies. When the individual cell 

 divides, . the two daughter cells do 

 not separate, but remain somewhat 

 loosely attached to each other, and the 

 process of division without separation continues until a con- 

 siderable group is produced. From this colony occasional indi- 

 viduals break awav and proceed to form new colonies. From such 



36 



Fig. 27. Magosphaera, a colonial 

 flagellate. 



