f^nridl Insects. G? 



divergence from Api^ in the absence of any particular dilation of the tibia 

 and metatarsus, tlie i)Osterior legs being similar to the anterior members, 

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

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

 less of [he pollen grains. The brush of the inner sui'face of the metatarsus 

 is still present, and in fact (jccui's in all Api(Ue and Andrenid^e. The genus 

 Nonuida is still less spi'cialized, in that the legs are simple, not dilated and 

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

 no ])ollen-collecting capacity. In this genus the brush t»f the metatarsus 

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

 as these bees are pseudo-parasitic or inquihnous 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 p(jl- 

 liniferous organs in various genera of the family A]iid;e, it will be seen that 

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

 entangle the grains of pollen. The iiext stej) 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 whicli the external hairs of both the tibia and 

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

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

 Anthophora, and consists in the partial disajipearance and shortening of tlie 

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

 l)erfect corbiculum is formed, foreshadowing the more complex sti'uctiu'e 

 of the social bees, in which it becomes (juite well ileveloped in Bonibus and 

 pei'fectly so in Trigona, Melipona, and Apis. In Anthophora a further 

 motlification is noted in that the hahs of the legs are practically simple and 

 unfeathered as in the higher social bees. 



In the other family of bees, the Andrenid;e, we have a similar condition 

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

 legs ranging from Aga|)ostemon to Prosopis, and showing the same grada- 

 tions noted in the Apid;e from Melissodes to Nomaila. 



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' works* on the subject. 

 There is almost an unbroken chaiu of these charactei's, from tlie 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 tieneath, occur 

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

 abdomen, the overlap] )ing half of each segment covering and protecting the 

 disc of the succeeding segment. With the Hive r>ee 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 sejKirated by an un- 

 modified medio- ventral sejitum. Tins 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 tlie segment, not being 

 V)roken, as in Apis, with a dividing septum, and also extending laterally 



*The Fertilisation of Flowers, by Prof. Hermatjn Mu'ller, Translated and edited by 

 D'Arcy "W. Thompson, B. A,, lyOndon, 1583. 



