216 FOUNDATIONS OF BIOLOGY 



to form a group which is set free as a miniature colony; but 

 in certain cases some of the reproductive cells become trans- 

 formed into male and others into female gametes. After 

 fertilization of the eggs, usually by sperm from another 

 colony, the zygotes develop into new colonies which even- 

 tually are liberated from the parent colony. (Fig. 18.) 



As has been previously suggested, the physiological divi- 

 sion of labor in the colonial Protista, involving, as it does, a 

 segregation of reproductive from vegetative structures, 

 affords a logical transition from the unicellular condition to 

 that characteristic of the multicellular forms. These, to all 

 intents and purposes, may be considered highly complex 

 colonies of cells in which specialization, no longer confined 

 merely to demarking germinal and vegetative regions, has 

 transformed the latter into a complex of tissues and organs, 

 the body (SOMA) of the individual, while the germinal tissue 

 (GERM) is confined to the essential reproductive organs. 



It is customary, therefore, to draw a more or less sharp 

 distinction between the soma and germ to consider the 

 soma the individual which harbors, as it were, the germ des- 

 tined to continue the race. This theory of GERMINAL CON- 

 TINUITY, which is chiefly associated with the name of Weis- 

 mann, recognizes that the germ contains living material 

 which has come down in unbroken continuity ever since the 

 origin of life and which is destined to persist in some form as 

 long as life itself. On the other hand, the soma may be said 

 to arise anew in each generation as a derivative or offshoot of 

 the germ; and, after playing its part for a while as the vehicle 

 of the germ, to pass the germ on at reproduction, and then 

 die. The germinal continuity concept has altered the attitude 

 of biologists toward certain fundamental questions in heredity 

 and evolution, as will be apparent when these subjects are 

 considered. (Figs. 115, 135.) 



