88 PROF. W. GARSTANG ON THE THEORY OF RECAPITULATION : 
10. Let US now take an equally unambiguous case of evolutionary change 
at the adult end oF the life-cycle. There is a group of genera of Geometrid 
moths in which the life-cycle terminates with normal winged males and 
more or less wingless females [Apocheima, Hyhernia, Theria*, &c.). It is 
an adaptive change, for, unlike their congeners which hibernate as pupre and 
emerge in early summer, these moths emerge in winter when the trees are 
leafless, and the normal method of repose is much more dangerous. The 
males, like both sexes of other related genera, rest by day exposed with 
wings outspread on tree-trunks, palings, &c. The wingless females 
hide in the crevices of bark. Both are active at night, the females 
creeping out of their crannies, and the males hunting for them up and 
down the woods. In the Early Moth {T. rupicapraria) and Dotted Border 
(S. marginaria), which emerge in February and March, the wings of 
the females are half as long as the body (South, ii. pi. 120) ; in the Scarce 
Umber (H. aurantiaria), which emerges as early as October or November, 
the wings are mere stumps (/. c. pi. 120) ; while in the Mottled Umber {H. 
defoliaria) and various other species the wings are completely lacking [I. c. 
pi. 122). The wings of the males are of full size throughout (Meyrick, and 
South, I. c). Now here is a case of evolutionary change of the adult form, 
and in one sex only ; but, with these facts before him, and with our know- 
ledge of the origin and breeding of similar mutations in Morgan's Drosophila 
experiments, who can assert that this abnormal adult has been added to the 
life-cycle of its normally-winged ancestors, and that the old adult has been 
" pushed back " to an earlier phase of the life-history. The wingless female 
is the exact counterpart of the normal male, and, though I do not know if 
any ch;inge has already taken place in the pupal characters of the female, it 
is a safe deduction from our knowledge of the pupal condition in more 
extreme cases to assert that the only changes likely to ensue will be in the 
direction of still further reducing the size of the pupal wings. The ontogeny 
will be influenced in the direction taken hy the new adult, and without regard 
to the ancestral adult at all. The new adult is just a modification of the old 
adult. There is no addition, no " tacking on" of a new stage ; no " pushing 
back " or " tachygenesis " of the old adult stage — merely a substitution of 
one adult type for another, and, sooner or later, some correlated changes in 
the stage which immediately precedes it. Zygotic mutations have caused the 
changes ; natural selection has controlled the breedings of successive 
generations ; and heredity has perpetuated the results of the selection. 
Certain ancestral adult characters are disappearing from the ontogeny ; and 
the condition of a flea, ontogenetically, as well as finally, without a trace of 
wings at any stage, is likoly to be the end result. 
11. I have selected this example, not because it is representative of all 
evolutionary changes that manifest themselves in the final stages of onto- 
geny, but because of its bearings on the most recent exposition of the theory 
* Meyrick's nomeuclature (1895); English names and figures in South (1908). 
