LIFE HISTORY 
and he is obviously correct in supposing it to be a pro¬ 
vision for the pushing away of the end of the puparium 
when the pupa emerges from its case. This frontal 
sac has been noticed by many observers, and was well 
described as long ago as 1764 by Count von Gleichen. 
Structure of the Adult 
In the section on zoological position, a description 
has been given of the characters which separate the 
adult typhoid fly or house fly from other allied or sim¬ 
ilar flies. The excellent illustrations given here (fig¬ 
ures 12 and 13) show in more or less detail its exact 
structure. Especial attention should be called, how¬ 
ever, to the character of the mouth parts and of the 
feet. The whole insect is more or less bristly and well 
capable of carrying micro-organisms from putrescent 
or semi-liquid substances, but the mouth parts and the 
feet are especially adapted to this purpose. In addition 
to two claws, each of the six feet is supplied with two 
sticky pads of a light color. These are called pulvilli. 
On the walking surface these pads are closely covered 
with hairs which secrete a sticky fluid, and it is by 
their help that flies are able to walk in any position 
upon highly polished surfaces. 
The mouth parts are very complicated, but form in 
the main a proboscis which is not fitted for piercing 
but for sucking and is illustrated so well in figure 15 
that detailed description will be unnecessary. This 
organ can be retracted and expanded to a certain extent. 
It is somewhat complicated in structure and consists 
