662 
J. DAViltSON. 
them as the mandibular setae (anterior setae), and maxillary 
setae (posterior setae). They are the “ Stechborsten,” “Russel- 
stilette,” etc., of German authors. 
The mouth or oral opening, which is not visible on external 
examination, is bounded by the oral appendages ; and two 
lateral growths of the wall of the head form a more or less 
enclosed buccal cavity round it. 
On the dorsal surface of the head is borne a pair of six- 
jointed antennae (a.), behind which, situated on the sides of 
the head, are the eyes (oc.). 
Distributed over the dorsal surface of the body are groups 
of wax-secreting glands [w.g.), the segmental arrangement of 
which is clearly indicated by the plate-like, facetted areas of 
the integument. These facetted integumental areas mark the 
position of groups of large unicellar dermal glands, which 
secrete the familiar masses of waxy threads. A pair of 
breathing pores, or spiracles, is situated on the ventral 
surface of the pro- and meta-thoracic segments {p.s.), [m.s.], 
but these structures are absent from the meso-thorax. There 
is also a pair of spiracles on the ventro-lateral surface of 
each of the first seven abdominal segments {a.s., 1-7). 
Two crescentic tubercles {cn.) are situated on the dorsal 
surface of the sixth abdominal segment. These structm-es 
represent the cornicles or “ honey tubes ” of other aphids 
such as Macrosiphum, etc. 
In addition to the openings of the body described above, 
there are two others, the anus {an.), and the genital orifice 
[g.o.], situated at the posterior end of the abdomen. The 
former lies beneath the small, ninth abdominal segment, and 
ventral to it, being separated by the anal plate (a.p.), is the 
genital orifice. 
On the ventral surface of the thoracic segments are seated 
the three pairs of ambulatory appendages, the first pair being 
the smallest, and the third pair the longest. 
The sense organs consist of a pair of small eyes (oc.), 
and two sensory pits (s. o.) situated on the two distal joints of 
each antenna. 
