32 THE PROBLEMS OF EVOLUTION 



individuals within a species has taken a new trend 

 in the formation of societies. This matter is ex- 

 ceedingly complex; in brief it shows that the 

 individual may give way as the unit to a more 

 complex association. The honey-bee colony is a 

 familiar and clear-cut example. In it we find three 

 types or castes, the queens, drones, and workers. 

 The queens and drones are incapable of securing 

 food or rearing young, yet they alone can produce 

 young; the workers are incapable of normal repro- 

 duction, but they alone can rear young, supply 

 food to the colony, and carry on the many neces- 

 sary accessory tasks. The colony here is the unit 

 of which the species is formed. No one would 

 question its reality or call it a mere concept for the 

 convenience of the beekeeper. The relationships 

 of the individuals within it are no more like those 

 of cells in a metazoon than like those of the indi- 

 viduals comprising a species, but they make up a 

 unit suflSciently restricted to be seen at a glance, 

 to be appreciated without the necessity of associ- 

 ating isolated facts. The limited existence, the 

 dependence, of individual honey-bees is reminis- 

 cent of the condition of fragments of cells or of 

 isolated tissue cells, but the fact that the colony 

 is an aggregation of structurally separate individ- 

 uals more closely approaches the nature of species. 

 The series of units here described show important 

 and significant characteristics. Cells may live as 



