THE ANATOMY OF THE ADULT MOSQUITO 81 



is well developed, but that of the last is ill developed, and 

 both are closely covered with short, downy hairs, and exhibit 

 also certain pits and specialised hairs, which probably are 

 sense organs, olfactor}^ tactile, &c. For further details on 

 the sense organs of insects, the reader is referred to 

 Lubbock's work, already quoted. Projecting from the 

 middle of the head {vide fig. 13), below the antennae, is the 

 characteristic proboscis which, although it at first sight 

 appears to be merely a cylindrical, trunk-like projection, is 

 really a very complex organ, being composed of no less than 

 nine separate pieces. The organ springs from a sort of 

 groove on the lower aspect of the head, through the inter- 

 vention of a flexible membrane, which admits of a certain 

 amount of protrusion and retraction as well as of flexion and 

 extension in the vertical direction ; the bases of both the 

 upper and lower lips being furnished with sets of longi- 

 tudinal and vertical transverse muscular fibres to effect 

 these motions. 



In all the Diptera the mouth parts of the adult insect 

 are modified, almost beyond recognition, from the obviously 

 trenchant jaws which have been already described in the 

 larva, and which persist, with but little alteration, through- 

 out life in some orders, such as the beetles. During the 

 three or four days of pupal life a marvellous series of 

 changes takes place, whereby the masticatory mouth of the 

 larva is transformed into the suctorial apparatus of the 

 adult. 



To understand the dipterous mouth it must be remem- 

 bered that, in most of the order, all that is visible to the 

 eye is the lower lip, the other parts being hidden, wrapped 

 up within it. Everyone who has handled a microscope is 

 familiar with the stock popular object of the " blow fly's 

 tongue." This "tongue" is the labium, and with the 

 exception of the maxillary palps, little else of the mouth 

 parts is in evidence, the other foot-jaws being but little 

 developed, as the fly licks rather than sucks its food, and 

 the "tongue" is provided with an armature of chitinous 

 rasps, not unlike those that stud the lingual rib, and of 

 gasteropod molluscs. If now we examine a horse fly, we 

 6 



