VARIATION 



409 



a hundred herrings, and so on. We register these observed 

 differences. 



It soon becomes plain, however, that analysis of our data 

 is necessary, if we are to avoid fallacy. We must try to sift 

 out peculiarities which are associated with age and with 

 sex, or are directly due to peculiarities of nurture. It is 

 obvious that immature herrings must be compared with im- 

 mature, and that we must not mix up the ruffs and the reeves, 

 drones and worker-bees. More difficult, however, is it to 

 separate off those peculiarities which can be experimentally 

 shown to be individually acquired modifications, directly due 

 to peculiarities in nurture (whether nutritional, environmen- 

 tal, or functional). Many crabs are profoundly changed by 

 being parasitised by Sacculina and related forms, and a 

 conclusion as to variability in crabs is vitiated by mixing 

 up the parasitised with the normal. An organism dwarfed 

 by lack of food or lack of space for exercise, such as the 

 fresh-water snails studied by Semper and De Varigny, is in 

 a different category from a normal dwarf appearing in a 

 family with no dwarfs in its recent lineage. The much cut- 

 up leaves of the fresh-water buttercup in the swiftly flowing 

 water, one of the examples Lamarck gave of the direct 

 results of environmental influence, are not to be placed 

 alongside of the laciniate leaves of a variety of the Greater 

 Celandine (Chclidonium majus} which cropped up without 

 warning in 1590 in an apothecary's garden in Heidelberg, 

 and has been breeding true ever since. 



Darwin called these directly induced, exogenous modi- 

 fications " definite variations " not a fortunate term ; they 

 are currently and unhappily called " individually acquired 

 characters " ; they are best called " somatic modifications ". 

 They may be defined as individual bodily changes directly 



