1900.] GROTE—THE DESCENT OF THE PIERIDS. 5F 
Despite, then, the preconception of authors, that their papers on 
their subject are final, yet it is seen that they are not so, and this 
from the complexity of the matter and the inability of the writer to 
look all around it. It was Dr. Johnson who said that the first care 
of the builder of a new system is to demolish the fabrics which are 
standing. Iam afraid this may be repeated of some of our work on 
the Lepidoptera, and that this demolition is notalways necessary. I 
should be sorry, however, to apply here the Doctor’s further opin- 
ion that thus the human mind is kept in motion without progress. 
At the end of the last century there seems to me to be a clear resi- 
due of advance. The truth of evolution conceded, the great fact 
that the biological is part of the geological process admitted, it 
might seem superfluous to attempt to gauge the flight of butterflies, 
were they not fellow-passengers across the scene, and could we not 
detect in their fate the shadow of our own. No witness can be 
thought unnecessary whose testimony, even if silent, bears on the 
problem of life. Undoubtedly in this way our interest in the con- 
tents of Natural History Museums increases the more we consider 
them in relation to ourselves. Indeed, this is the deeper reason for 
the existence of all collections. 
To return to our tables of genera: it is but too certain I can 
offer no such complete scheme of the Pierids as Sir George Hamp- 
son has given us of the Syntomids. Setting aside the incomplete- 
ness of my material, I do not know if Pontia, for instance, is 
surely an Anthocharid, or belongs to the typical line of Prerts. I 
do not even know if there is anybody who could tell me, so con- 
tradictory appears the evidence, and there are a number of ques- 
tions, perhaps less crucial and more easily satisfactorily solved, as to 
which I am in doubt, and to resolve my doubts by drawing firm 
lines on a plan I am incapable. Bya hundred points do these frail 
insects impinge on their surroundings and fade away into space. 
All that I can try to do is to see that the names along a horizontal 
line represent forms conforming, barring immeasurable inequali- 
ties, to a certain approximate grade of specialization, while those, 
in the same vertical line, succeed one another in the expression of 
one of the movements which I have elsewhere shown to occur in the 
position and number of the veins of the wing. Thus the succes- 
sion represents ideally the probable or possible sequence in time 
and space. I use generic names only in connection with the struc- 
ture of the type. 
