334 Mr. A. Radcliffe Grote on the Changes in the 
goes a parallel process, z.e., the reduction of the radial 
veins by a process of absorption in the more specialized 
forms.* Thus, among the Pieride, the Cabbage butter- 
flies have a three- to four-branched radius, in the Yellows 
the radius has four veins, whilst in Anthocharis and 
Leptidia the normal five branches attain the margins of 
the wing. A parallel case is offered by the Blues, where 
the four radial veins of Iycena are reduced to three in 
Thecla. It is evident that these characters, repeating 
themselves as they do in otherwise different groups, are 
insufficient to warrant the view of a near relationship 
between the forms exhibiting them. They are characters 
of convergence, and, therefore, secondary in their nature. 
At the same time their presence in different groups proves 
the essential unity of the process of development or 
evolution in the wings. 
The second direction, in which the progress of sim- 
plification manifests itself, is in the disintegration of the 
median series of veins. In some T'ineides the main stem 
(or stems) of the media, between the base of the wing 
and the cross-vein, which serves now as the point @appur 
for the three median branches (veins iv}, ivy, and iv3), is 
present. But in the butterflies, as well as in most of the 
moths, this stem has disappeared, or is represented 
merely by scars upon the surface of the tegument of the 
median cell. The former passage of these stems along 
what is now an unbroken surface is indicated by slight 
processes, apparently emerging from the cross-vein 
closing the cell at its outer extremity and turned towards 
the base of the wing in the direction in which the stems of 
the media appear to have formerly lain. ‘The suppres- 
sion of these stems has been evidently the first step 
towards the abolition of the median series which, in the 
day butterflies, asserts its existence only through the 
three branches arising from the cross-vein and attaining 
the outer margin. We have now to consider the fate of 
these three branches, and to see what becomes of them 
during the evolution of this portion of the wings. 
In the case of the absorption of the radial veins we 
found that the condition of the hindwings of most recent 
* T learn from my friend Dr. Hofmann that an intermediate form 
between the five- branched and one-branched radius of the secondary 
has been discovered in the Tineide. 
