73 
* 
% 
to the resemblance. Very few species of this family have been dis¬ 
covered, and so far they have never been known to be injurious in thi.. 
C °The insects belonging to the family Psyllidas bear a strong 
reseinblaame to the true Plant-lice, having much the same form 
and somewhat similar, transparent 
wings. The differences may be un¬ 
derstood by comparing the annexed 
fio-ure of Psylla pyri with figures oi 
true Plant-lice shown further on. The 
antennse are split into two slender 
bristles at the tips; the front wings 
have one principal vein which di- 
vides near the base into three bran- 
pheseach of which again forks, and rig. 12 . Fsyiiapyn. 
the hind wings have several radiating veins; the head is as broad as 
the thorax and the abdomen is small compared with the rest of the 
body. In addition to these characters they also possess the powei of 
leaiiing and hence have been named “.Jumping Plant-lice. 
Th e Aphid* or true Plant-lice do not possess the power of leaping 
the antennae are without the two bristles at the tip, but the terminal 
joint is often slender and bristle-shaped, and the - v "™ally t X fi. ee • 
nr seven ioints but are sometimes reduced to five or e\ en ti > 
sometimes thev considerably exceed the body in length but are some¬ 
times much shorter. The wings are very delicate and membranous, 
and usually transparent; a strong rib or vein courses along near the 
front which, in the typical species sends off three , bra ™ b f ™’XrI 
obliauelv backwards toward the hind margin; the outer or tuna 
branch usually gives off near its middle a fork running toward the 
tip which often again forks before reaching the margin, as in. Fig-^ 
In some species there is but a single fork, as in ■ ig. , me 
third branch is simple and not forked, as in Figs. 15 and 16, m ..0 
species the third branch vein is wholly wanting, as in I ig. 1/. 
The hind wings usually send off two posterior branches fiom 
rib'iSi » JSK in Fin.. 18 14 and 15 ; but in 
is but one, Figs. 16 and 17, and in one group there is no branch e - 
As a general rule the wings when at rest are placed above the back 
in the form of a very steep roof, but there are some species in which 
thev lie horizontally on the abdomen when at rest. 
I® i !,* ■ 
1 
