64 ON THE AGAMIC REPRODUCTION AND MORPHOLOGY OF APHIS 
In an embryo sth of an inch in length (Pl. XXXVIII. [Plate 3] 
fig. 1, 1a, and 2), the procephalic 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 antennz have greatly elongated, and are bent downwards and 
inwards, so as to meet in the middle line below, and cover the 
mandibles. 
The first maxilla are larger than the mandibles, and somewhat 
expanded at their extremities. The second maxilla are more 
slender; and their bases are in a line with those of the mandibles, 
while those of the first maxilla 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 maxille. 
The thoracic members have greatly elongated, the hinder pair 
being the longest. 
In embryos ;4,th of an inch in length (P]. XNXVIII. [Plate 3] 
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 ex- 
tended ; and so thoroughly has this extension taken place, that the 
abdomen is now convex inferiorly. 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 procephalic 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 posterior margin of the head on 
each side. 
If the appendages be examined as they become metamorphosed 
in a succession of specimens intermediate in size between ,3,th and 
;'gth of an inch, the antenne are found gradually to increase in length 
and to become jointed. The growth of the mandibles and first 
maxilla in length, on the contrary, is suspended ; and they remain 
as short thick tubercles (Pl. XXXIX. [Plate 4] fig. 2), from whose 
inner surface a long chitinous filament gradually arises. These 
filaments, thickening and elongating, become the blades of the 
mandibles and maxilla. The growth of the second maxilla makes 
up, by its excess, for the arrest of development of the mandibles and 
first maxille; for having already approximated, their confluent or 
connate bases elongate as one great process, which extends back in 
the middle line between the thoracic legs, until at length it attains 
