126 THE THEORY OF MUTATION 



by a few marked variations, each of which occurred 

 simultaneously in all the feathers at once, several 

 serious difficulties are avoided, and on the analogy of 

 similar known cases we have every reason to believe 

 that this was so. And similar changes may take place 

 in cases where the pattern depends on the coloration 

 of a group of feathers or hairs. Indeed, if we con- 

 sider, we shall find it very difficult to picture such a 

 process as taking place in any other way. We can 

 scarcely suppose the spots of the leopard, for instance, 

 to have arisen one at a time. 



An important kind of discontinuous variation is 

 that to which Bateson has applied the term homceosis. 

 The same sort of change had previously been described 

 by Masters in the case of plants under the name 

 ' metamorphy,' but the latter expression has also 

 been employed in other senses. Homceosis consists 

 in the assumption by one member of a meristic series 

 of the form or character proper to another member 

 of the same series ; for example, the modification of 

 the petal of a flower into a stamen, or of the eye of a 

 crab into an antenna-like organ. 



' In these cases a limb, a floral segment, or some 

 other member, though itself a group of miscellaneous 

 tissues, may suddenly appear in the likeness of some 

 other member of the series, assuming at one step the 

 condition to which the member copied attained pre- 

 sumably by a long course of evolution.' * 



The phenomenon of homoeosis is frequently to be 

 seen among the parts of flowers. Double flowers in 

 * ' Materials for the Study of Variation,' p. 570. 



