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 Uke a pocket-knife. 



Hermann Miiller ('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, i 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. 



I. 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, s) draws back the mentum, and with it the Hgula, so far that the laciniae 

 reach as far forward as the labial palps (to the point u 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. 



