Mr. J. J. Weir on some points of resemblance, dc, 269 



surmounted in some cases by beautiful oval floating leaves, 

 about two-thirds of an inch long, like those of a Potamogeton ; in 

 others, by pure white three-petalled flowers, also floating on the 

 water. The slender thread-like stalks, curled and twisted, follow 

 the rise or fall of the level of the water, so variable in mountain 

 lochs. In the same water was a peculiar form of Juncus supinus, 

 with very slender flaccid leaves and stalks, perfectly erect, and 

 without runners ; the flower-heads very small, and with a 

 distinct pinky colour, reminding one of Epilobium buds. It is 

 Juncus flnitans, Lamarck. 



85. — On some points of Eesemblance between certain 



DiPTERA AND HyMENOPTERA. 



By John Jenner Weir, F.L.S., &c. 

 (Read Sept. 10th, 1890.) 



Since Mr. Bates drew attention, many years ago, to the 

 mimicry of one species of butterfly by another, the subject has 

 received considerable attention from those who delight in the 

 philosophy of natural science ; and his hypothesis that the 

 model was a species inedible by birds or lizards, and that the 

 edible obtained a certain amount of impunity from their attacks, 

 by its deceptive resemblance, has received general acceptation. 



The insects in the box, herewith, illustrate another kind of 

 mimicry, inasmuch as they are species of Diptera, or two-winged 

 flies, which feed on the larvae of hymenopterous humble-bees. 



The whole of the specimens exhibited are of one species, but 

 it will be seen that the four upper closely mimic the common 

 humble-bee, Bombus terrestiis ; the three in the centre, the red- 

 tailed humble-bee, also a very common species, Bombus lapidarius. 

 The single specimen, at the bottom of the box, illustrates 

 imperfect mimicry ; the specimen is black, like the mimic of 

 Bombus lapidarius, but its abdomen at the extremity is of a 

 whitish yellow instead of red, in this respect more resembling 

 the mimic of Bombus terresttis. 



It is very probable, as pointed out in the ' Entomologist's 

 Monthly Magazine,' by Colonel Blathwayt, that this mimicry 

 enables the flies to deceive the bees, and thus pass into their 

 nests and deposit their eggs in the comb, where the larvae of the 

 flies are parasitic on those of the bees. 



The subject is a very interesting one, and should be further 

 investigated, in order that it may be ascertained that the 

 dimorphic forms of the Volucella do really affect the nests of the 

 two species of bees they respectively resemble. 



c2 



