282 Dr. Frederick A. Dixey on the 
species of Catasticta ; and in these also the red or orange 
of the costa is a prominent feature. In other species of 
Pieris a farther alteration has taken place, and the 
markings have been swept from the basal portion of the 
wing (as in P. demophile), or away altogether (P. bumiz). 
In most, however, if not all of these cases, the precostal 
streak persists, again taking a yellow rather than red or 
orange colour; and, in the absence of other yellow or 
well-defined dark marks on the wing, it comes to 
resemble very closely the corresponding feature in so 
many species of Synchloe and Ganoris. 
Summary.—The facts adduced in the course of the 
foregoing remarks seem so far to allow of little doubt 
as to the history of the yellow precostal streak. It is 
evidently a survival of a series of yellow or orange marks 
which is found, in many genera of both eastern and 
western Pierinze, on the underside of the hindwing, 
partially or wholly oceupying the paler areas left between 
the relics of the original dark ground colour. The 
greater number of these marks may disappear with a 
general lightening of the wing, or the whole wing may 
become so yellow as to render them almost or quite 
indistinguishable ; but the particular yellow streak that 
occupies the margin of the precostal space is more per- 
sistent than any of the others, and may remain, as in our 
common species of Ganoris, after every other character- 
istic of the ancestral marking has departed. It will be 
seen later that this account of the precostal streak, 
though no doubt correct as far as it goes, in all pro- 
bability needs supplementing. 
b. The red basal patch.—In both British species of 
Ooclias, there occurs at the base of the hindwing, on the 
under-surface, a pinkish patch, which occupying the 
apices of the cell and of the median and submedian 
interspace, and also in most cases asmall area at the root 
of the precostal space, is often prolonged for a short 
distance along the middle of the cell. This patch, which 
is almost always present throughout the genus Colias, is 
found in most if not all species of Meganostoma, and 
also very commonly in Catopsilia, Callidryas, Phebis, 
Aphrissa, and Metura. It is present, too, in Dercas, 
Gonepteryx, Rhoducera, and Amynthia; in these, however, 
it does not as a rule extend far from the body itself. 
Beyond the limits of these closely-allied genera this 
