PARASITES. 227 



in half, they proceed, like Miinchausen's horse at the well, but at 

 length they withdraw the proboscis from the wound, fly staggeringly 

 away, and die within a few minutes/' 



I may add that the late Henry Seebohm told me on his return 

 from Siberia that he was very much troubled by the mosquitoes 

 settling on his gun-barrel when he was about to fire, rendering it 

 most difficult to take a careful sight. 



Heredotus also relates (Enterpe^ XCV.) that the Egyptians, 

 who lived in the marshy grounds, used to sleep under their fishing 

 nets in order to escape from the attacks of gnats, of which he tells 

 us there were surprising numbers. 



The gnats have aquatic larvae and pupae. The eggs are laid on 

 water and the larvae float at the surface, head downwards, so that 

 the respiratory organ, which is at the other end and contains two 

 air-tubes, is flush with the level of the water, and feeds and 

 breathes uninterruptedly. When it passes into the pupal form, 

 the position is reversed. It floats head upwards and breathes 

 through two trumpet-shaped organs attached to the thorax. The 

 gnat belongs to the sub-class Holotnetabola^ having a complete 

 metamorphosis, the larva, pupa, and imago differing much from 

 one another. 



The fleas of which I am about to speak also belong to the 

 same sub-class, having a complete metamorphosis. 



In the flea, the mouth-parts consist of a lingua, which may be 

 taken to represent the upper lip, and two mandibles with a central 

 rib, and serrated edges, protected when at rest by the labial palpi, 

 and which unitedly form the piercing apparatus, thus constituting 

 a tubular haustellum. There are also maxillae at the sides of the 

 mouth, of a somewhat triangular form, furnished with rather large 

 five-jointed palpi, which have been mistaken for antennae. The 

 antennae are usually carried in receptacles at the back of the eyes, 

 these receptacles being covered by movable valves. At times the 

 antennae may be withdrawn from their cavities. The lingua is 

 toothed on the upper surface and traversed throughout its entire 

 length by a canal, which gives off smaller ones, terminating at the 

 end of the teeth, thus constituting the suctorial organ. On most 

 of the fleas infesting the lower animals one or two pectinate fringes 

 are found. On the dog-flea, one is on the lower part of the head 



