376 Annals Entomological Society of America [Vol. VIII, 
categories are already well known. We have, for instance, (a) 
cases where there appears to be a simple difference in the size 
of all parts simultaneously, (b) cases where in the ontogeny of 
an insect certain parts gain their growth at a different period 
than others and the conditions affecting general size may 
show most prominently in these organs and (c) cases where the 
tendency to abnormal growth seems limited to certain organs 
and the adjacent parts profit or suffer through this abnormality. 
This list of categories will have to be enlarged and sub- 
divided as investigations will show necessary until we can 
recognize the nature of the variation in the growth of organs 
or portions of the body that brings about all the differences: 
we observe in size and form. 
Surface differentiations result from variations in the secretion 
of cuticle by the individual epithelial cells and should be 
expressed in terms of these activities. Often a very definite 
relationship between the surface modifications and the form 
of the parts of the body may be recognized. The most evident 
categories are (a) where the cells over the whole sclerite or 
specialized organ produce a homogeneous cuticle, (b) where 
an equally definite relationship exists but with bordering or 
concentric specializations, (c) where the structural modification 
has relation to general body structure rather than to individual 
sclerites and (d) where the modification conforms to an internal 
structure, particularly muscle attachments. 
The qualities of the surface modifications we express by a 
large series of Latin adjectives describing the mass effect 
of these cuticular differentiations. These adjectives should be 
redefined in terms of their ultimate structure in the individual 
cells and subdivided as found necessary where the same super- 
ficial appearance is the result of essentially different 
modifications. 
The accurate quantitative statement of surface structure 
will become possible as soon as progress 1s made in the more 
logical study of the topographic and qualitative differentiation 
just suggested. 
Color and pattern, like surface structure must be studied 
as the resultant from the activities of individual cells, but 
is not wholly a question of pigment as has already been amply 
shown nor wholly of epithelial activity. Our classification 
