SEGMENTATION OF THE BODT. 
21 
formed from the eighth^ the lateral appendages 
(“ Afterlappchen ” of Kaltenbach) as the ninthj the 
anus and anal plate as the tenth, and the cauda as the 
eleventh segment, respectively. 
Thus, typically, the head represents six somites. 
Of these, the caput proper, the antenna, the labium, 
with its sete, may be assigned to three. The other 
three somites are indicated by the three joints of the 
rostrum or haustellum. The thorax next is composed 
of three somites, as indicated by the pro-, meso-, and 
meta-thorax previously described. These, when added 
to the eleven abdominal segments, complete the 
typical number of twenty.* 
It often happens that several abdominal rings of the 
larv^ are so united by their sutures that their number 
cannot be distinguished. This is markedly the case 
when the Aphis has been struck by an Aphidius, or 
other parasitic insect. The larva then appears much 
like an inflated and shining bladder, supported on 
six legs. 
On the under side of the abdomen,- generally from 
seven to eight rings can be distinctly counted, ex- 
cluding the genito-anal region. 
Below the lateral edge, formed by the Connexivum, 
the Stomata or apertures leading to the tracheal or 
respiratory system are placed. These occur at the 
sutures of the various rings, and typically should be 
ten in number. They are not always easily recog- 
nised, but in some light-coloured species their position 
may be detected by certain dark stains or punctures. 
The Stomata are always placed on the under side of the 
body, and appear to be of the simplest character, 
seemingly without fringes or operoula. 
The Stomata present either circular or oval aper- 
tures, which are kept distended by a horny ring. 
Every segment has its appropriate pair, with the 
exception of the head. One is placed close to the base 
of each cornicle, 
* Vide figure o£ a typical Aphis after Huxley, PI. B, fig. 5. 
