Social Insects. 67 



divergence from Apis in the absence of any particular dilation of the tibia 

 and metatarsus, the posterior legs being similar to the anterior members, 

 simple in structure, and armed with long, scattered, feathered hairs, which 

 are generally distributed over all their surface and which entangle more or 

 less of the pollen grains. The brush of the inner surface of the metatarsus 

 is still present, and in fact occurs in all Apidre and Andrenid;e. The genus 

 Nomada is still less specialized, in that the legs are simple, not dilated and 

 also practically hairless ; or rather the hairs are short and simple and have 

 no pollen-collecting capacity. In this genus the brush of the metatarsus 

 can hardly have any other use than to keep the body of the insect clean, 

 as these bees are pseudo-parasitic or inquilinous and do not collect or store 

 pollen. It is a mere modification of the normal or original structure and 

 doubtless a degeneration due to the semi-parasitic habit. 



From the above review of the modification of the posterior legs as pol- 

 liniferous organs in various genera of the family Apidye, it will be seen that 

 there are first developed on the leg, hairs which are feathery and which will 

 entangle the grains of pollen. The next step in the development is an in 

 crease in the abundance of this hairy vestiture, and a further advance 

 occurs in the widening of the tibia and first tarsal joint, to give a greater 

 surface for the pollen-collecting, plumose hairs. This reaches its maxium 

 in the genus Melissodes in which the external hairs of both the tibia and 

 the metatarsus are very long and dense and the feathering very decided. 

 The next step toward the condition found in Apis is exhibited in 

 Anthophora, and consists in the partial disappearance and shortening of the 

 hairs on the outer face of the tibia and metatarsus, by which means an im 

 perfect corbiculum is formed, foreshadowing the more complex structure 

 of the social bees, in which it becomes quite well developed in Bombus and 

 perfectly so in Trigona, Melipona, and Apis. In Anthophora a further 

 modification is noted in that the hairs of the legs are practically simple and 

 unfeatherecl as in the higher social bees. 



In the other family of bees, the Andrenidpe, we have a similar condition 

 of things, the variation in the pollen-collecting character of the posterior 

 legs ranging from Agapostemon to Prosopis, and showing the same grada 

 tions noted in the Apidse from Melissodes to Nomada. 



The reader interested in studying how the mouth-parts and the legs have 

 been modified in the bees by their honey and pollen gathering habits, can 

 not do better than consult Hermann Miillers' w T orks* on the subject. 

 There is almost an unbroken chain of these characters, from the highly de 

 veloped bees to such as are hardly distinguishable from the fossorial wasps. 



NOTE 4. Wax- producing organs. 



In all the wax-producing bees the specialized discs (see Fig. 3) on which 

 the wax is deposited when secreted by the true glands beneath, occur 

 on the basal half of the second to the fifth ventral segments of the 

 abdomen, the overlapping half of each segment covering and protecting the 

 disc of the succeeding segment. With the Hive Bee these discs are com 

 pound and two in number on each segment. They are broad, ovate, pale 

 yellow in color, smooth, delicate and transparent, and are surrounded by a 

 narrow thickening of the chitine of the sclerite and separated by an un 

 modified rnedio- ventral septum. This specialized structure occurs only in 

 the workers. The queen, however, has a sub-obsolete, undivided area on 

 the same five abdominal segments, and which in structure bears a striking 

 resemblance to the similar area in the workers of the lower forms of social 

 bees. The wax discs of Melipona and Trigona are practically identical, and 

 are narrow, extending entirely across the base of the segment, not being 

 broken, as in Apis, with a dividing septum, and also extending laterally 



*The Fertilisation of Flowers, by Prof. Hermann Muller. Translated and edited by 

 D'Arcy W. Thompson, B. A,, L,ondon, 1883. 



