28 CHARACTERS OF THE LARVA. 



first. The second, third, and fourth form the thorax, and 

 the remainder belong to the abdomen. The relative length 

 and thickness of the abdomen varies much in different species. 

 The skin is, as a rule, very soft, and is usually whitish, although 

 it is sometimes thick and almost leatherlike, and is occasionally 

 intensely coloured. 



' The mouth armature of the headless larvae is very simple, 

 and consists of two black pointed hooks near the anterior part 

 of the head. That of the eucephalic larvae can be distinguished 

 in certain species as consisting of an upper and under lip, 

 mandibles, maxillae, and even maxillary palpi, as in the larvae 

 of the Coleoptera. In the eucephalae simple eyes, antennae or 

 their rudiments, and false feet are usually present. The latter 

 are conical truncated organs provided with hairs or hooks, 

 situated on the ventral surface of the annuli of the body, and 

 used in some species as organs of progression. The larvae of 

 a few spring by the elongation and rapid contraction of the body. 



' In some the stigmata or breathing pores are found on the 

 middle rings, peripneiistic larva ; in others they only occur on 

 the first and last segments, amphipneustic larva?, or are confined 

 to the last segment, mctapncustic larva;.' 



They are either terrestrial or aquatic, and exhibit very great 

 variations of form. Many eucephalic larvae have a pair of false 

 feet on the first thoracic segment, and these and the abdominal 

 false feet may be provided with spiny cushions or suckers. 

 The nervous system consists of thirteen ganglia, two cephalic, 

 three thoracic, and eight abdominal, but sometimes these are 

 concentrated into two nerve-centres (Brauer). 



Brauer says, ' The recognition of the mouth organs in the 

 larva is very difficult, owing to the very unequal development 

 of the head ;' he does not attempt to determine the com- 

 parative morphology of the hooks and tubercles which form 

 the mouth armature of the acephalae, but suggests that the 

 great hooks of these are maxillae (Unterkiefer ?) [14, p. 33]. 



It has long been known that the head-capsule amongst 

 many of the eucephalae is very rudimentary, and Hammond, 

 I think, first demonstrated that this is due in the Crane-flies 



