26 
BEITTSH APHIDES, 
are nearly suppressed, or are entirely wanting, the tail 
also is mostly small, or altogether absent. Some 
genera show this organ free, and distinct from the ring 
to which it is an appendage, but other genera have a 
power of retracting it, more or less, within the cavity 
of the body. 
On this account I have not laid so much stress upon 
the value of its length, as Passerini has done, who 
measures its length against that of the cornicles. 
The colour of the Gauda is pretty constant in spe- 
cies, and therefore should be noted. 
Below the anal plate, two darker coloured opercula 
or valves occur, which close the vaginal orifice, and 
constitute the Afterlappchen ” of Kaltenbach, who 
takes advantage of their difference in colour for dis- 
criminating species. 
The terminal abdominal rings of the males differ 
much from those of the females. Two papillw occur, 
which have offices similar to the claspers of other 
insects, and also tend to strengthen the very curiously 
formed male organ, when it is protruded.* 
The description of the ano-genital apparatus will 
be comprised in a later section of this Monograph. 
THE WINGS. 
In by far the greater number of cases the males and 
viviparous females of Aphides are provided with four 
wings, by which they transport themselves into other 
localities, either in seach of fresh food, or for the 
purpose of founding new colonies. Some species of 
the Mhizohiidm or root inhabiters have, so far as we at 
present know, no alate forms. Other species, few in 
number, do not complete their metamorphosis in this 
country, yet do so abroad. To quote an example, 
Ghaitophorus salicivora^ so plentiful on our willows, is 
known here only in its immature form. 
* Vide Plate B, fig. and Plate Xlb fig- 5. 
