476 the president's address. 



higher order through the process of colony formation and integra- 

 tion, and that it is quite impossible to draw hard and fast lines 

 between the successive terms of the series. We have seen also 

 that even amongst highly organised plants and animals individua- 

 lity does not depend upon the preservation of the same identical 

 parts in the same association. Individuals may be subdivided 

 and joined together in a variety of ways, and parts of different 

 individuals may be interchanged without impairing their vitality. 

 In short, we can by no means frame a general morphological 

 definition of individuality. 



Are we any better off* when we ask what constitutes an 

 individual from the physiological standpoint ? A criterion of 

 individuality is indeed often sought in the power to perform all 

 the essential vital functions, or, in other words, to live a com- 

 pletely independent life. A unicellular organism does everything 

 for itself. It feeds, respires, gets rid of its waste products and so 

 forth, all in a very simple but at the same time efficient manner. 

 A single cell of one of the higher plants or animals, on the other 

 hand, though it may live independently for some time in a 

 suitable medium, cannot do so indefinitely. It has sacrificed the 

 power of doing everything for itself to the power of doing some 

 one particular thing more efficiently, and depends for its con- 

 tinued existence upon the co-operation of innumerable other 

 cells. Similarly, a single highly specialised individual of a 

 siphonophoran colony, such as a swimming bell of Physophora, 

 is quite incapable of independent existence ; from the physio- 

 logical point of view the colony as a whole constitutes the 

 individual, though the morphologist has little difficulty in 

 recognising the component members. 



This leads us to the consideration of certain other cases of 

 great interest. Many of the higher animals, though they do 

 not form colonies in the morphological sense, have the habit of 

 living together in social communities which we might regard as 

 colonies of completely separated individuals. The honey bee is 

 a familiar example. In a hive of bees we find individuals of 

 three kinds, easily distinguishable from one another both by 

 habits and by structural peculiarities. The queen is a perfect 

 female, and is alone capable of laying eggs. The ordinary 

 workers are imperfect females which have sacrificed the power 

 of reproduction and concentrate their energies upon the collection 



