NUMBER or MOULTS 97 



superficial, all the parts present in Psorophora (Janthinosoma) sayi, for in- 

 stance, being easily traceable on close examination in Psorophora ciliata, the 

 shape only being altered. The mandibles have the toothed area well developed, 

 the hair-fringe much reduced. 



Lutzia is derived from Culex, from the more generalized part of that genus. 

 The maxillae have a generally quadrate shape, but the modification from the 

 usual Culex type is not great. The median suture is still distinct, the papillaB 

 are present, even the crown of hairs is represented by shortened appendages. The 

 mandibles have the toothed area well developed and terminally placed owing to 

 the reduction of the other parts. 



Though the three genera above mentioned, MegarMnus, Psorophora and 

 Lutzia, are all predaceous with their mouth-brushes, the individual hairs of the 

 brushes are differently modified in each, as would be expected from the inde- 

 pendent evolution of the predaceous habit in the three cases. 



MOULTING AND NUMBER OF LARVAL STAGES. 



The larvas of mosquitoes have four stages, that is, they moult four times, 

 transforming to pupa with the fourth moult. Apparently the number of moults 

 is constant and is the same for all species. The newly hatched larvae already 

 show all the organs of the mature larva but they are much simpler. The chiti- 

 nization of the head and breathing tube are less evident and complete than in 

 older larvae. The breathing tube is only chitinized in its apical portion and the 

 chitinous plate of the anal segment is very small. The principal hairs present 

 in the older larvae are already found on the first-stage larva ; but all of them are 

 simple, whereas in the later stages many of them become composite. The ventral 

 brush of the culicine larvas is absent in the first stage. The first-stage larva may 

 be recognized by the presence, on the head, of the egg-burster. This is situated 

 dorsally on the middle of the head and consists of an oval, pale, depressed area 

 in the middle of which is situated a chitinous disc surmounted by a small, black, 

 chitinous peg. 



When the larva is about to moult the hairs of the following stage may already 

 be seen beneath the skin. The long hairs of the sides of the thorax and abdomen 

 are wrapped about the body transversely and show as transverse blackish lines. 

 Immediately after moulting the color of the chitinous parts is pure white; 

 gradually these assume their characteristic color. The approach of the last 

 moult may be recognized by a number of changes in the appearance of the larva. 

 The coloration of the body becomes more opaque. Most striking is the increase 

 in the size of the compound eyes, these becoming gradually drawn out dorsally 

 into a sharp point until they nearly meet upon the median line. This change 

 is particularly striking in the Sabethini where the compound eyes do not become 

 evident until late in larval life. A short time before pupation two dark spots 

 appear on the thorax, dorsally at the anterior angles. These are produced by 

 the breathing trumpets of the pupa lying underneath. 



The moulting larva or pupa makes its escape from the old skin through breaks 

 in the dorsum of the head and thorax. The head splits open along the epicranial 



