MOSQUITOES AND TSETSE-FLIES. 
17 
ward garbs ; but from whatever point of view they may be 
regarded, they illustrate the difficulty, augmenting as know- 
ledge increases, of defining and limiting the meaning of the 
term " species," of such constant use in natural history. 
In the middle line of the hall is placed a case containing Mosquitoes 
greatly enlarged models of Mosquitoes or Gnats and of an p^^J^^^^^' 
African Tsetse-Fly ; also still more enlarged gelatine models of 
mammalian blood-corpuscles, showing the parasites by which 
they are infested in the diseases respectively communicated 
by means of Mosquitoes and Tsetse. Models of the parasites 
themselves are also shown. 
Malaria or ague is a disease peculiar to man. It is caused 
by extremely minute parasites which live in the red corpuscles 
•of the blood. Formerly malaria was believed to be contracted 
by merely breathing the air of marshy districts, but it is now 
proved that the parasites are transmitted from man to man 
by the bite," or rather stab," of a Mosquito or Gnat. The 
common Mosquito or Stabbing Gnat {Culex pipicns) does not 
transmit the malaria parasite; the Spot-winged Mosquitoes, 
of the genus Anopheles, abundant in England and nearly all 
parts of the world, are the carriers of the malaria parasite. 
This parasite multiplies not only in the human blood, but in the 
stomach and tissues of the Gnat — as shown in the models. 
Tsetses are African blood-sucking Flies, with the mouth-parts 
adapted for piercing the skin of mammals such as Antelopes 
and Zebras. The blood of some of these animals is infected 
with a parasite, which, when carried adherent to the proboscis 
of the Fly, and introduced by its bite into the blood of domesti- 
cated animals such as the Horse and Ox, produces the fatal 
Tsetse Disease. The model of one of these flies exhibited is 
28 times (linear) natural size ; the Tsetse parasites and the red 
blood-corpuscles are enlarged 6,000 diameters. 
The Tsetse parasite multiplies in the blood by the longi- 
tudinal division of each of the individuals. 
Most of the bays or alcoves round the hall, five on each Bays or 
side, are (with the exception of the one at the north end of ^Je°HalL 
the right side reserved for the exhibition of recently acquired 
specimens of especial interest, and the middle one on the 
^ame side, which is at present occupied by illustrations of the 
G 
