27 
slide, but a cabinet of objects ; in fact, a printed catalogue lay by 
the side of the microscope for reference to any particular valve. 
He also exhibited live caterpillars of the emperor moth; very 
gorgeous crystals of hematoxylyn, the colouring matter obtained 
from log-wood ; artificial alizarine, prepared from an oil of coal 
gas (the discovery of this substance is regarded as a great triumph 
in chemistry, as it resembles the red dye obtained from madder) ; 
polyzoa, and other interesting objects. 
In addition to these microscopic objects, Dr. Hatiirax 
exhibited a number of beautiful microphotographs of his own 
taking ; and Mr. J. Howstt, pebbles picked up on the beach, 
shewing encrinites, pentacrinites, bryozoa, cidaris spines, &c. 
June 9th.—On ‘‘ Diptera and their Wings,” by Mr. PEAKE. 
While wings are common to the whole order of insects, the 
Diptera consist entirely cf two-winged flies, which, instead of a 
second or hinder pair of wings, have little thread-like bodies, 
terminated by knobs; these are called Halteres, were originally 
considered balancers, but are now supposed by some to be olfactory 
organs, by others organs of hearing. 
From many points of resemblance, he thought they were 
analogous to the hind wings of insects, and that, at present, their 
special use had not been ascertained. Besides the Halteres, they 
also had winglets (alule), which were thought to be only append- 
ages to the fore wings. 
Among the Diptera, three classes of flies were found, differing 
in the form of their bodies and the shape of their wings ; first, 
the slender flies, such as gnats, having long bodies, narrow wings, 
and long legs, but without winglets ; secondly, those whose bodies, 
though slender, are more weighty, as the Asilide, having larger 
wings, shorter legs, and very minute winglets ; lastly, those like 
the house-fly, with short, thick, and often very heavy bodies, 
furnished with proportionate wings, shorter legs, and conspicuous 
winglets. From these circumstances it might be inferred that the 
long legs of the light-bodied flies acted as rudders, while the 
