AND MORPHOLOGY OF APHIS. 223 



their base so as to form a sort of oUjow. In consequence of this, theii* terminal portions 

 are more approximated than their distal ones, and lie close together and parallel. These 

 appendages are the antennae ; 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 cephaHc 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 (iv') are the largest, 

 and are the mandibles ; the two other pairs are nearly equal : the anterior (v') represent 

 what are ordinarily termed the maxillae, but which might be more properly called 

 "first maxillEe," since the second pair- (vi'), which eventually give rise to the so-called 

 " labium," are precisely like them, and, as Zaddach {I. c. infra) has shown, fully deserve 

 the title of " second maxillae." 



Three pairs (vii', viii', ix') of short processes, unjointed and not much longer than the 

 troj^hi, represent the thoracic limbs. 



The abdomen presents obscm-e traces of a division into segments. 



In an embryo -^ih. 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 antennae 

 have greatly elongated, and are bent downwards and inwards, so as to meet in the 

 middle line below, and cover the mandibles. 



The first maxillae are larger than the mandibles, and somewhat expanded at their ex- 

 tremities. The second maxillae are more slender ; and their bases are in a line with those 

 of the mandibles, while those of the first maxillae 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 

 maxillae. 



The thoracic members have greatly elongated, the hinder pair being the longest. 



In embryos T^^th of an inch in length (PI. 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 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 towai'ds the 

 posterior margin of the head on each side. 



If the appendages be examined as they become metamorphosed in a succession of spe- 

 cimens intermediate in size between xo^th and T^jth of an inch, the antennae are found 

 gradually to increase in length and to become jointed. The growth of the mandibles and 

 fii-st maxiUae in length, on the contrary, is suspended ; and they remain as short thick 

 tubercles (PI. XXXIX. fig. 2), from whose inner sui-face a long chitinous filament gra- 



