INDIVIDUALS AND SPECIES 29 



though it is composed of lesser units whose reaHty 

 is also generally admitted. 



The relation of a species to included individuals 

 is, of course, not identical with the relation of an 

 individual to its component cells, but are individ- 

 uals an end in themselves? They may exist alone, 

 to be sure. An asexual or parthenogenetic indi- 

 vidual is even a sufficient unit for a time. If per- 

 petual life were possible it might remain so, but 

 the life of the individual under any circumstances 

 is limited. Asexual or sexual, it must sooner or 

 later die or merge its existence with that of the 

 offspring which it produces. It is inevitably asso- 

 ciated in some way with other individuals of its 

 kind. These may be very different from itself, 

 whence the difficulties arising from polymorphism, 

 or they may be essentially the same, but the asso- 

 ciation always occurs. The aggregate of these asso- 

 ciated individuals is the species. 



The reality of the species is necessarily different 

 from that of the individual, yet it, too, is an aggre- 

 gation of units. The unit individuals are con- 

 stantly changing, and they are not usually con- 

 nected with each other or wholly dependent upon 

 each other like the cells of the body. From year to 

 year and from generation to generation no species 

 ever embraces exactly the same constituents, yet 

 it continues to exist. Until reduced to a very lim- 

 ited compass, such as the last dozen passenger 



