AND MORPHOLOGY OF APHIS. ; 223 
their base so as to form a sort of elbow. In consequence of this, their terminal portions 
are more approximated than their distal ones, and lie close together and parallel. These 
appendages are the antennæ; and it is worthy of remark, that they arise from the proce- 
phalic lobes, or from the point of junction between them and the rest of the cephalic blas- 
toderm above the mouth. 
Behind these and behind the mouth (though the anterior pair are very close to that 
aperture, and might even be described as more or less lateral in relation to it) are three 
pair of short, similar, conical processes. Of these the anterior pair (1v') are the largest, 
and are the mandibles; the two other pairs are nearly equal: the anterior (v') represent 
what are ordinarily termed the maxillæ, but which might be more properly called 
“first maxille," since the second pair (vr), which eventually give rise to the so-called 
“labium,” are precisely like them, and, as Zaddach (2. c. infra) has shown, fully deserve 
the title of * second maxille.”’ 
Three pairs (vir, VIT, IX’) of short processes, unjointed and not much longer than the 
trophi, represent the thoracic limbs. 
The abdomen presents obscure traces of a division into segments. 
In an embryo y5th of an inch in length (Pl. XXXVIII. fig. 1, la, and 2), the pro- 
cephalic lobes have extended so far back as completely to cover the tergal region of the 
head, and even to pass a little beyond the line of the last maxilla posteriorly. The 
fold or depression separating the thorax from the head has become deeper; the antennæ 
have greatly elongated, and are bent downwards and inwards, so as to meet in the 
middle line below, and cover the mandibles. 
The first maxillæ are larger than the mandibles, and somewhat expanded at their ex- 
tremities. The second maxillæ are more slender; and their bases are in a line with those 
of the mandibles, while those of the first maxillæ have taken a more external position. 
Consequently, the bases of the trophi, instead of forming two nearly parallel rows as at 
first, are now arranged as a hexagon, whose outer angles are constituted by the first 
The thoracic members have greatly elongated, the hinder pair being the longest. 
In embryos 7th of an inch in length (Pl. XXXVIII. fig. 5), the blastoderm is found 
to have undergone a wonderful change. Instead of being folded upon itself ventrally 
by the flexure of the abdomen against the thorax, it has become completely extended; 
and so thoroughly has this extension taken place, that the abdomen is now convex in- 
feriorly. At the same time the blastoderm has grown upwards over the sides of the 
body, and roofs-in its tergal region. The head is closed by the union of the procephalie 
lobes, and is now, in consequence of the increased length of the body, proportionally 
much smaller. The pigment of the eyes appears in a few scattered granules towards the 
pig yes app 
posterior margin of the head on each side. 
If the appendages be examined as they become metamorphosed in a succession of spe- 
eimens intermediate in size between roth and „th of an inch, the antennæ are found 
The growth of the mandibles and 
gradually to increase in length and to become jointed. . hort thick 
first maxillæ in length, on the contrary, is suspended; and they remain as short thic 
.. tubercles (Pl. XXXIX. fig. 2), from whose inner surface a long chitinous filament gra- 
