2 GNATS OK MOSQUITOES — CHAPTER I 



and the appendages and jaws are so little specialised, that it 

 is commonly spoken of as being acephalous. 



It is obvious that this division, though associated with 

 fundamental structural differences, is of little value to the 

 observer who possesses only the perfect insect, but none 

 of the Gyclorrhapha are at all likely to be confused with 

 Mosquitoes, and the sub-divisions of the Orthorrhapha are 

 marked by characters of a very obvious sort in the adult 

 insect ; the Sub-order being divided in a very natural 

 manner, into two sub-divisions, by the characters of the 

 antennao. In the Nematocera, to which the Culicidce 

 belong, the antennae are large and prominent organs, con- 

 sisting of more than six joints, and the palp of four or five 

 joints, while in the Brachycera the antennap are of in- 

 significant dimensions, consisting of but two or three 

 apparent joints, and the palpi are also but one or two 

 jointed. Osten-Sacken further sub-divides the Nematocera 

 into the true and the anomalous groups of families. The 

 true Nematocera, which include the Cecidomyidce, Myceto- 

 philidco, GtilicidcG, Chironomidce, TipuUdce, Psychodidcn, and 

 possibly the Dixidcc, have the following characters : — 



(1) The eyes are never blended into a single mass, and 



there is little or no difference in the size of the 

 head and eyes in the two sexes. 



(2) Eyes round, oval or lunate; they may meet but 



never blend. 



(3) Antennae very large in proportion to the small head. 



(4) Legs long and weak, not fitted for walking. 



(5) Generally slighter, and more slender. 



(G) Inhabit damp, shady places, and prefer twihght. 



The anomalous Nematocera, which include the Simulidce 

 or sand-flies, the Bihionidce, dc, on the other hand, are 

 characterised as follows : — 



(1) Head generally holoptic in both sexes, nearly always 



so in the male. 



(2) Eyes often bisected, the upper facets being the 



largest. 



(3) Legs well adapted for walking and often thick. 



(4) The sexes generally differ considerably. 



