6 K. Takaliashi 



iJu! adults, hut usually :ir(^ fowor-jointed in (.lie young nyinphs than in the grown 

 ones or adults. In the first instar tliey are usually 4 or 5, rarely 3, but nuver 

 6-jointcd. According to Davis, the first instar of the first generation of 3f(icrosiphiini 

 piai Kalt. has the antennae fewer-jointed than in the corresponding instar of other 

 generations. In the fully-grown nymphs they usually have as many joints as in the 

 adults. The mode of joint-multiplication is the same in all species. The new joint 

 is derived from the third joint, not from others, and only one joint may be added at 

 any one moult from the first to the fourth, as shown by the accompanying table. 

 Each joint of each instar is usually longer than the corresponding joint of the prece- 

 ding instar, but the third joint of the second or third instar is sometimes shorter 

 tjian that of the preceding. The basal two joints are always very short and 

 stout as in the adults; they correspond to the scape, and the remaining joints to 

 tlio flagellum, iu other insects. The first joint, in the genus A^cojAorodon. is furni- 

 shed with a tubercle, smaller than those of the adults, on the inner side. The third 

 joint is destitute of hairs in the first instar, but is provided with them in the later, 

 in the genus Macrosiphnm. The secondary sensoria are almost always absent in the 

 immature stages, but the gro\\u nymphs of some Dllaclmus, Lachnus and Eulachniis 

 are furnished with a few such sensoria on the fourth or fifth joints. Each of the 

 last two joints is always provided witli a primary sensorium, which in some species 

 is surrounded by a row of hairs. Even in tlie first insfeir the last joint is also 

 provided with some smaller sensoria situated in a group beside the primary senso- 

 rium; the filament or spur is as in the adults. 



The thorax is very simple in structure, since no sclerites are distinguishable 

 even in the mesonotum of the fully-grown nymphs of the winged form. In Oregma, 

 Ccratajthis, Astegopter>/x, Aleurodaphis, NeopJiTjUdjJiis, Ccrvnphis, Grcenided and 

 others, as already mentioned, the pronotum and the head are usually defined in the 

 fourth instar and adults of the winged form, but they are fused together in other 

 instars of it, as well as in all the stages of the wingless form. 



In the genera Aph.is and lihopalosiphum, the prothorax is furnished with a 

 small lateral tubercle even iu the first instar. In the third instor, the mesothorax 

 of the winged form begins to develop, protruding laterally, becoming larger, with 

 the wing-pads well-developed in the fourth instar. 



The wing-pads are usually dusky or pale greenish in coloui, always without 

 liairs and wax-pores, and are plai ed close to the sides of the thorax, especially in the 

 Callipterina. TJie hind p.dr of pads is always smaller, being completely covered by 



