80 
INTRODUCTION TO 
been already explained, and further details will be 
given hereafter. 
Whenever the larvae are provided with oral organs 
formed for suction, the same conformation obtains 
in the prefect insect ; but suctorial species are often 
produced from masticating larvae. In the former 
case the nature of the food scarcely varies in the 
whole course of the animal’s existence ; in the latter 
it must necessarily be quite dissimilar. The various 
parts of the mouth, as well as other appendages of 
the head, are analogous in form and function to those 
that exist in the imago. An upper and under Up, 
mandibles and maxillae, and from two to six palpi 
can be distinguished ; antennae and eyes (the latter 
generally of the simple construction,) are likewise 
present, in far the greater number of cases. The 
mandibles vary in form and consistency according to 
the nature of the substances upon which they are 
designed to act: in many carnivorous tribes they 
are long and curved j and in Dytiscus, Hemerobius 
and Myrmelion, they have another and a singular 
function superadded to then’ ordinary uses : they are 
perforated throughout their whole length, and thus 
form a tube through which the animal sucks the 
juices of the prey which it has secured by their 
means. Among many Diptera, the mandibles serve 
as instruments of motion ; the larva fixing its poste- 
rior part to the plane of position, and then stretching 
its body in advance, seizos some point of support 
with its jaws, and by their aid easily drags the body 
