154 INTRODUCTION 
while the development of a membranous lappet on the tip of the ligula presumably 
renders it possible to lick up flat layers of nectar. 
Just as the pollen-collecting apparatus has reached its highest degree of 
development in Apis and Bombus, so also has the mouth of these bees become best 
adapted for rifling the nectar of flowers. It is therefore intelligible that bees belonging 
to these two genera play a far more important part than any other insects in the 
pollination of our indigenous flowers. 
Graber (‘ Werkzeuge der Tiere,’ II, p. 213) rightly says that what makes the 
humble-bee proboscis so marvellous is not so much its individual parts, as the way 
in which these are united into a complete whole. Considered as a mechanism the 
proboscis is a tube composed of several long splints (and therefore dilatable) within 
which the actual receptive organ, i.e. the ligula) moves up and down. This tube 
or sheath of the ligula consists of the two-grooved laciniae above, and the labial 
palps below. At the base of the proboscis, the cavity of this sheath passes into 
a canal formed by two gutter-like basal pieces of the maxillae and labium, and 
is finally connected with a curious pumping-apparatus situated within the cranial 
capsule. The suctorial proboscis of the humble-bee, and Hymenoptera generally, 
is interesting to us not only because it is so constructed that it can be widened and 
narrowed, but also because, by means of a highly specialized mechanical arrange- 
ment, it can be closed like a pocket-knife. 
Hermann Miller (‘Fertilisation,’ pp. 58-64) gives an exhaustive description of the 
proboscis of bees and other Hymenoptera, with a thorough account of the functions 
of its various parts. When the mouth-parts of Apis and Bombus are fully extended 
and artificially separated (Fig. 66, 1 and 2), it seems at first sight hardly possible 
that a suctorial apparatus so large and complex, which is occasionally several 
times as long as the head, and in certain species even exceeds the body in 
length, can be completely received into a cavity below the head’, as is the case 
with’ the short proboscis of the less specialized bees. Yet this takes place with 
great ease and certainty by means of the four folding movements already mentioned. 
We must now consider the relation of these movements to the diverse activities of 
the proboscis. 
1. When the bee is sucking nectar which is only just accessible, all the movable 
joints of its suctorial apparatus—cardines, the chitinous retractors at the base of the 
mentum, laciniae, labial palps, and ligula—are fully extended as in Fig. 66, except that 
the two proximal joints of the labial palps are closely applied to the ligula below, and 
the laciniae to the mentum and hinder part of the ligula above. But as soon as the 
whorl of hair at the tip of the ligula (which is extended as far as possible, and sunk 
to the bottom of the flower-tube) is wet with nectar, the bee by rotating the retractors 
(Fig. 67, 2) draws back the mentum, and with it the ligula, so far that the laciniae 
reach as far forward as the labial palps (to the point w in Fig. 66); and now 
laciniae and labial palps together, lying close upon the ligula and overlapping it with 
* It is only in the case of exotic bees (e.g. Anthophora fulvifrons and Euglossa in Brazil) that 
the proboscis is so long that even repeated folding is inadequate to conceal it on the under-side of 
the head. In such cases the protruding part lies on the ventral surface of the body along the middle 
line, and in Euglossa even reaches to the end of the abdomen. 
