134 THE THEORY OF MUTATION 
many cases—for instance, in the case of the rose—arise 
by the development of petal-like organs in the position 
which would properly be occupied by stamens. A 
parallel process is‘ to be seen in the heads of com- 
posite flowers, such as the chrysanthemum. In a 
double chrysanthemum the florets of the disc develop 
in the likeness of ray florets. Both these cases would 
be classed as examples of outward homeosts, because 
the parts concerned resemble organs normally de- 
veloped in a whorl exterior to themselves. A case of 
inward homeosis, on the other hand, is afforded by 
the appearance of a petaloid calyx—for example, in 
a tobacco-plant—the outermost whorl of the flower 
taking on the appearance of a whorl internal to itself. 
In cases such as these we observe once more the 
occurrence of a marked and definite change, which, 
though at first sight quite distinct from the method of 
similar and simultaneous variation, yet bears a certain 
resemblance to that process in the fact that the direc- 
tion in which a particular part varies is not wholly 
unrelated to the behaviour of other parts of the same 
organism. The process thus briefly described seems 
likely to have had considerable importance in evolu- 
tion, notably in the origin of differences in the numerical 
relations of the bones in various parts of the spinal 
column in different vertebrate animals. 
The preceding account of the conclusions drawn 
from Bateson’s laborious study of variation has in- 
volved a good deal of technicality, but this is, un- 
fortunately, unavoidable. The point chiefly to be 
emphasized is the frequent occurrence in Nature of 
