PHYTOPHTHIRES. 
741 
division), in the immobile nymph firmly protected by a ‘ scale 5 and 
living gregariously fixed to one part of the plant. 
In Coccidce, the parasitism is at its height; in a number we find that 
parthenogenesis is a frequent occurrence, that the nymph is active only 
in the youngest stage, that the female is a simple sac, producing eggs, 
that a scale or other covering is present and that the male alone is free- 
living and winged ; the insects live gregariously fixed to the plant and 
viviparous reproduction is not uncommon. 
Until the physiology of the pupal period is investigated in greater 
detail it is impossible to judge how far the metamorphosis is 
really perfected, but there is a growing differentiation, both in 
the Phytophthires as a whole and in Coccidse themselves of the 
metamorphosis, though the wings are developed outside ; there is 
not quite a sudden change from the wholly apterous nymphs to 
the ‘ pupa 5 with large free wing-rudiments, since the insect makes 
its cocoon after the last nymphal moult (not before, as in truly 
metabolous insects) and since it is active after the pupal moult and 
can move away to shelter before the wing pads emerge ; but the whole 
process of wing development and of c metamorphosis 5 takes place not 
during the last three instars as in most Homoptera, but during the 
last alone, the insect being then immobile. This is, in essence, an 
incomplete but advanced metamorphosis, and if we regard Coccidce 
as being linked on to the Homoptera, then we must regard the 
Phytophthires as showing a growing tendency to a metamorphosis 
and thus to an approximation to the higher and metabolous insects. 
We are of the opinion that the group show a marked adaptation to 
a £ parasitic ’ existence, visible in the differentiation of the male 
metamorphosis and in the simplification of the female life, the first to 
secure the perfect winged form, the latter to secure the undifferentiated 
egg-sac. If this view be correct, the division is moving, not to an 
approximation with higher forms, but to an increased degradation, 
an adaptation to an inactive and parasitic existence. There is, how¬ 
ever, no reason to believe that Coccidce have sprung from a separate 
stock as some would have us believe, and we may regard them as 
being the present apex of one branch of the Homoptera. 
