iv] THE SECOND GRADE 99 



them taken at random a whole new individual will 

 organize itself. 



After this examination of such a compound in- 

 dividual, we must now turn and trace the method by 

 which this second grade of individuality has been 

 built up, the method by which the Metazoa have 

 evolved from Protozoa. The step from first to second 

 grade is one of the two or three most important in 

 the whole history of life ; yet it has taken place 

 successfully on several different lines, and unsuccessful 

 attempts are many. 



Among the Protozoa, as among almost all other 

 groups of animals, many species live in colonies- 

 using the word colony to mean a collection of 

 organisms all similar to each other, and all united 

 either by living substance or by some framework that 

 the living substance has secreted. 



Such colonies are not higher individuals in any 

 sense of the word, but it cannot be denied that 

 they already possess certain properties on which the 

 higher individuality can be grounded. A colony, 

 besides possessing a characteristic shape, forms a 

 single whole, separate from all other similar wholes ; 

 this separateness, as has been seen, is a necessary basis 

 for the exclusively or almost exclusively physical 

 individuality of the lower organisms. As regards 

 function, however, the members of the colony often 

 retain as perfect an independence as they would have 



72 



