16 BEACHYCEBA. 



whilst at the other end of the scale, i. e., those larvae with unduly 

 large heads, the term eucephalous is applied. The eucephalous 

 kinds are the less common, but they are the normal form in the 

 nematocerous family Ctjljcidte. The head in the larva) of the 

 majority of brachycerous families exhibits an intermediate type 

 between the extreme forms. Many kinds of larvae have retractile 

 heads, the front part being completely withdrawable inside the 

 following segment or segments. 



Regarding the mouth-parts Brauer, roughly speaking, described 

 the larvae of the Nematoceba as having the jaws moving 

 horizontally, except in cases where the mouth-parts are quite 

 rudimentary, when the larva is peripneustic and 13-segmented. 

 He claims for the Bbachyceea vertically moving jaws — sucking 

 and boring groups coming also under this division, the head being 

 not well developed. Brachycerous larvae with rudimentary mouth- 

 parts are amphipneustic or metapneustic, with ten to twelve 

 obvious segments. 



The number of body-segments is frequently by no means easy 

 to ascertain, Br. Sharp stating that there is "no morphological 

 criterion yet discovered by which the segments can be numbered.*' 

 In some cases, of course, they are obvious enough, whilst in others 

 there are what have been termed intercalary segments, apparently 

 consisting of the undue development of the integument between 

 the orthodox segments, the ]avv& of the Thebeyldje and Soeko- 

 pusidje being instances in which the apparent number of segments 

 approximates to about twenty. The larva with the smallest 

 number of segments appears to be that of the nematocerous 

 family Beephaeoceeid2e, in which only five or six are present. 



Locomotion is usually effected by means of pseudopods, as 

 jointed legs are unknown through the whole order of the Diptera, 

 these pseudopods being transverse swellings on the under (or 

 sometimes both upper and under) surface of the body, and they 

 may also be furnished with rows of bristles or small wart-like 

 projections, placed on a varying number of segments according to 

 the species. 



The spiracles in Dipterous larvae consist of a posterior pair 

 placed near or at the tip of the body, where there is often some 

 special development for their protection. Larvae with only one 

 pair of spiracles, the posterior ones, are called metapneustic ; but 

 if in addition there is a pair of anterior ones placed a little behind 

 the head, they are termed amphipneustic: whilst when intermediate 

 spiracles are also present, making, so to speak, three sets in all, 

 they are known as peripneustic. 



The pupa-case is ordinarily the dried larval skin, the imago 

 escaping through a longitudinal split occurring between two 

 transverse splits, normally on the ord and 5th segments re- 

 spectively. 



Further detailed information will be found under the respective 

 families or genera concerned. 



