80 INTRODUCTION TO 



been already explained, and further details will 

 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 animaFs 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 lip, 

 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 their 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, seizes some point of support 

 with its jaws, and by their aid easily drags the body 



