part u.] THE INSECTS WHICH VISIT FLOWERS. 49 
cardines of the maxille (¢¢, 4, Fig. 11), are hinged by two joints to 
the sides of the cavity below the head, so that they can rotate 
backwards and forwards. In the state of rest they are bent back- 
wards ; the next segments (stipites) (st), and the mentum which is 
placed between, are drawn back, so as to cover the cardines 
completely. The lamin of the maxille (/a), with their palps 
(pm) and the labial palps (p/), are also folded over, downwards 
and backwards, and the mandibles (md) are laid over the bases of 
these parts, and also cover the retracted tongue (/i) and the down- 
ward-folded upper lip (/br, 2, Fig. 11). In the state of rest, the 
mandibles alone are free to act, without any other part of the mouth 
changing its place. When they are separated (2, Fig. 11), the 
upper lip, the tongue, the bases of the retracted maxille, the 
maxillary and labial palps, come into view. 
fs When the bee wants to suck honey, it extends its maxille and 
_ maxillary and labial palps forwards, and spreads out its tongue 
_ (3, Fig. 11); then turning the cardines of the maxille forward 
(¢ c, 4, Fig. 11) on their hinges, the maxillz and labium (mentum 
and tongue) are advanced by twice the length of these cardines, 
and the tongue may now be introduced into honey-receptacles if 
not too deep or narrow. 
The Sand-wasps possess in quite a similar manner the power of 
_ folding up the lower parts of the mouth to bite, and extending 
- them to suck, and so Prosopis can show no advance in fitness 
_ for a floral diet beyond the ancestors of the bees. The only 
peculiarity which Prosopis has developed is the habit of lining its 
_ brood-cavities with slime, which hardens into a thin shell; this 
_ habit necessitates a short, broad tongue, and therefore prevents 
_ the development of a long tongue fitted for obtaining deeply- 
_ seated honey. 
Considerably higher in the scale than Prosopis, in regard to 
_ such adaptations, are Sphecodes, and the closely allied, but still more 
_ specialised genera, Halictus and Andrena. In all three, the tongue 
_ (li, 4, Fig. 12; 1, Fig. 13) is moderately short, and is enabled to 
reach more deeply-placed honey, not so much by its own length as 
by the increased length of the mentum and the cardines. Unlike 
Prosopis, the tongue here is pointed, and more or less covered with 
hairs and fine transverse lines at the tip; since it has become 
more freed from the task of nest-building,! it has grown narrower 
and more elongated in many species of Andrena and Halictus, to 
* These genera line their brood-cavities, which are generally subterranean, with 
very little slime. 
E 
