iv] THE SECOND GRADE 101 



they are joined, however, the motion of the couple is 

 no longer similar to the motion of its two components. 

 Mathematically it is the resultant of their two motions, 

 and as such depends on the way in which the two 

 individuals are attached to each other. If the action 

 of their locomotor organs is not fixed and invariable, 

 it will also depend on the way in which these are 

 used by the two individuals. 



Hence for the couple to move, it is essential that 

 the motions of its two parts shall not neutralize each 

 other, but that they shall be co-ordinated to give a 

 resultant motion useful to the whole couple. 



Then there is the resistance of the Avater to be 

 considered, so that before a colonial organism can 

 move effectively its parts will have to acquire a 

 shape, an arrangement, and a mode of action, 

 differing from those Avhich had served them perfectly 

 Avhen they Avere independent beings. 



The further step necessary before the colony can 

 \vith full right be called an individual is the differ- 

 entiation of its members so that they perform different 

 functions. As with the primitive homogeneous lump 

 of protoplasm (p. 57) so Avith the "homogeneous 3 ' 

 colony of similar members ; both are on the Avay 

 to acquiring an individuality for themselves, both 

 exhibit features Avhich are the necessary foundations 

 of that individuality, but neither can Avith justice 

 be said to possess it. 



