HYMENOPTERA—BEES 153 
Prosopis, feeble in Sphecodes, more clearly visible in Halictus) are represented by 
prominent transverse rings over the greater part of the worm-like ligula. The hairs 
on the ligula, which scarcely present any definite arrangement in the lowest stages 
mentioned, form regular whorls on each transverse ring that can be erected and 
forwardly depressed. And, lastly, the movable membrane connecting mentum 
and cardines is extended and supported by chitinous bars, in such a way that 
when these fold together the mentum is retracted between the stipites as far as 
the ends of the cardines, while when the chitinous bars unfold it is protruded 
for their full length. 
Certain modifications of the maxillae are inseparably connected with these 
specializations of the labium, so that the same successive stages can be recognized 
in both groups of bees. As soon as the ligula is so far lengthened that it can 
no longer be retracted into the anterior hollow of the mentum, it is folded up 
downwards and backwards when not in use, and both in the retracted and protruded 
condition is sheltered between the laciniae so as to be protected from injury during 
nest-building and the process of penetrating into nectar-receptacles. The laciniae 
having come to serve as a sheath for the elongating ligula must therefore extend 
in the same proportion. The labial palps elongate similarly, in order that they may 
continue to act as tactile organs, and when the ligula is not too long this is also the 
case with the maxillary palps. The latter, however, are soon outstripped by the 
continually elongating laciniae, labial palps, and ligula, and ultimately degenerate, 
while the laciniae and labial palps keep pace with the ligula even to its highest 
degree of elongation. The difference between the changes undergone by the 
maxillary and labial palps, which originally had the same function, is explained 
as follows. With increasing elongation of the ligula, the laciniae become modified 
to form a sheath, closely enveloping the ligula, and protecting it from injury, both 
when retracted and also while being inserted into flower-tubes. During the sucking 
of nectar the laciniae also assume the réle of a suction-tube, in which the nectar 
probably passes to the mouth by the successive erection of the whorls of hairs on the 
ligula, from the tip upwards. The labial palps are also pressed into the service of 
this curious suctorial apparatus, by the flattening of two or three of their basal joints, 
so as to help the laciniae in the close sheathing of the ligula, the last joint or two, how- 
ever, retaining the original tactile function. This explains the elongation of the basal 
joints of the labial palps, which keep pace with the growth of the ligula and laciniae. 
They become long, thin, chitinous plates enveloping the ligula, while the still tactile 
end-joints retain their original form and shortness, as well as their free external 
position. The six-jointed maxillary palps, on the other hand, having been out- 
stripped by the elongating laciniae, are handed down merely as useless appendages, 
and therefore present all stages of degeneration from six joints to none at all. 
A final increase in the length of the ligula, beyond that of the structures which 
ensheathe it, is attained by making the proximal part of this worm-shaped organ 
(which is fused with the paraglossae) coil twice round when retracted into the hollow 
end of the mentum. The ligula, therefore, when drawn back, reaches just to the end 
of its sheath, but when fully protruded projects to a distance about equal to the 
length of the sheath. The sucking-apparatus of bees, greatly elongated in the way. 
described, is also adapted for boring juicy tissues by the sharpening of the laciniae, 
