16 INSECTS NOXIOUS TO AGRICULTURE. 
of Aphis are seen two erect more or less prominent tubes, called 
“ cornicles”’ or “ nectaries,” and it is the function of these to 
excrete the honeydew.* No European entomologist has, it is 
believed, seen or described the organ of honeydew-excretion in 
the Coccidide. Some observations by the author of this work 
in 1886 demonstrate its existence as a cylindrical tube exserted 
from the ano-genital orifice after the manner of a telescope, the 
furthest-extended tube being the most slender. This organ, 
extremely difficult of detection when not in use—except in the 
single genus Celostoma—is at intervals pushed out to its full 
extent, and at its further extremity there appears a minute 
globule of yellowish, nearly transparent, glutinous fluid, which 
rapidly expands like a soap-bubble, and then, suddenly breaking, 
falls in spray on the leaf beneath. In the second stage of the 
female of Cclostoma zelandicum this organ may be detected 
more easily than in any other Coccid; but the act of protrusion 
of the organ and the formation of the drop of honeydew are 
apparently by no means frequent, and many long observations 
may be made without witnessing either.t (The organ and the 
honeydew-drop are shown in Plate xxii.) 
For the purposes of this work further details as to the 
production of honeydew are not necessary. But as to its effect 
on plants it is requisite to be more particular, and the attention 
of tree-growers and gardeners is specially directed to the follow- 
ing points. It has been said above that when the bubble of 
honeydew has been expanded to its full size it breaks into spray. 
Now, as a general rule, Coccids are found almost exclusively on 
the wader sides of leaves (when not on the bark). Some, as 
Lecanium hesperidum and a few others, may be seen on the 
upper side; but the general rule is as here stated. It follows 
that the spray of honeydew from the burst bubble falls, not on 
the leaf where the insect is, but on the upper sides of the leaves 
below it. These upper surfaces, being more exposed to light 
and air than the lower ones, are usually deserted not only by 
the Coccids but by other insects also, and so there is not much 
* The fluid also emerges from the anal orifice; but, seemingly, no mention 
is made by any observer of any special honeydew-organ protuding from the anus 
of Aphis. 
+ Mr. Comstock (‘‘ Report on Insects,” U.S. Dept. of Agric., 1881, p. 22) states 
that on gently rubbing a Dactylopiws two small drops of fluid, which he con- 
siders to be honeydew, can be seen to emerge from orifices on the dorsal side of 
the sixth abdominal segment; but he mentions no special organ in the body 
The experiment has been tried on Dactylopius in this country without success. 
