DISCONTINUITY OF SPECIES n 



tude, are all capable of changing the general appear- 

 ance of a plant so as to render it scarcely recognisable. 

 Fortunately, in the case of the higher plants, the 

 floral organs, which are the ones chiefly made use of 

 for purposes of specific discrimination, are very little 

 liable to modification by external conditions ; but 

 in the corals a similarly stable set of organs does 

 not appear to have been discovered. It seems, there- 

 fore, hardly fair to regard the example of the corals 

 as affording an established exception to what we 

 must look upon as the general rule namely, that 

 species are on the whole definite and discontinuous 

 groups. 



As a rule, then, the species riddle presents itself 

 definitely as the problem of the existence of a series 

 of discontinuous groups of creatures, sharply marked 

 off the one from the other, and often, too, existing 

 among surroundings which afford no corresponding 

 discontinuity, though each is well enough fitted for 

 the life which it has to lead. 



The problem which we have to face has been 

 enunciated by Bateson in the form of the two following 

 propositions : 



* i. The forms of living things are various, and on 

 the whole are discontinuous or specific. 



' 2. The specific forms on the whole fit the places 

 they have to live in. 



' How,' he continues, * have these discontinuous 

 forms been brought into existence, and how is it they 

 are thus adapted ? This is the question the naturalist 

 is to answer. To answer it completely he must find 



