December 2, 1889.] 



KNOWLEDGE 



29 



on each side of it are the mandibles, in the form of two 

 straight flat blades, pointing downwards, and notched on 

 each side like a double saw. The mandibular teeth 

 number about 7.5 in each row on each side, wliich, at the 

 rate of two double rows to each mandible, gives a total of 

 some 600 glistening tooth-like projections on these 



J mb 



Fig. 2. — Mouth Organs of Flea ; s, labrum ; mh, man- 

 dibles ; mx, maxilla ; mp, masillaiy palpi ; //i, labial palpi. 



weapons alone. The maxillfe are two sharp-pointed trian- 

 gular pieces, which, when seen in profile, as ni a specimen 

 mounted for the microscope, have the ajipearance of a 

 sharp beak ; they are furnished with a pair of long four- 

 jointed palpi, which project in front of the head, and 

 might easily be mistaken for antennw. The labium is 

 reduced to a small membranous plate, which carries a j^air 

 of palpi, not quite so large as those of the maxill* ; each 

 of these is formed into a keen blade on one edge, and 

 rather obscurely jointed into four on the other. It is not 

 easy to say cxartly how these organs are used, since when- 

 ever we are consciously subjected to their operation, w^e 

 are more anxious to get rid of the operator than to examine 

 minutely into its method of proceeding. The whole 

 evidently constitutes a piercing apparatus of exquisite 

 delicacy, and the mandibles are no doubt the most effec- 

 tive part. We are accustomed to speak of rlcahitca, but 

 this is scarcely a correct way of designating the operation ; 

 the appendages of the mouth are not in any sense biting 

 organs ; tlie action is tliat of vertical piercing, not lateral 

 pinching or nipping. In possessing palpi fleas agree with 

 flies, and differ entirely from the other chief order of in- 

 sects with a piercing, suctorial mouth, viz. the bugs, which 

 are never provided with such organs. On the other hand, 

 in possessing both labial and maxillary palpi they differ 

 from the ordinary flies, which are furnished with the latter 

 only. 



In the structure and arrangement of their organs of 

 sense, again, fleas justify our statement that they are 

 zoological oddities. While the eyes of flies are compound, 

 each mass often containing thousands of facets, those of 

 fleas are simple, and consist only of one rounded knob on 

 each side ; and as most of tlic insects' predatory operations 

 are carried on in either partial or total darkness, it would 

 seem that even these numerically reduced visual organs are 

 of no great avail in the obtaining of food. The eyes are 



3. — Antenna of Dog'; 

 After Landois. 



Fi.EA (Pules 



placed in the ft-ont of a hoUow space, in the hinder part of 

 which the antenna' are lodged ; these are short, curiously 

 shaped organs, and are so obscurely situated that they 

 woiild certainly escape notice unless carefully looked for. 

 (Fig. 3 represents the antenna of a dog's flea, and that 



of the human pest 

 is verv simOarly 

 shaped.") The hol- 

 low in which they lie 

 is partially covered 

 by an extension of 

 the chitinous inte- 

 gument of the head, 

 and the part still 

 left open is further 

 protected at a lower 

 level by a mem- 

 branous flap, which 

 can be pushed aside 

 when the antemiae 

 are protruded. Then- 

 extraordinary shape, 

 as well as their con- 

 cealed and guarded 

 position, indicates 

 that many mterest- 

 ing problems await 

 solution as to their 

 functions and the 

 particular uses of 

 the several parts. 



The last two tho- 

 racic segments carry 

 a rounded scale on 

 each side, projecting 

 from their hinder edge. The first is a minute one, but 

 the second very much larger, overlapping parts of the first 

 two abdominal segments. They are apparently rudimen- 

 tary wings. 



Fleas sometimes exist gregariously on then- hosts, and 

 those of the lower animals especially have the habit of 

 attaching themselves most pertmaciously to some part of 

 the body fi-om wliich no eflbrt of their host can dislodge 

 them. Some years ago, ilr. Verrall exhibited before the 

 Entomological Society a colony of li\-ing fleas which had 

 been taken shortly before from the inside of a rabbit's 

 ear, where they were congregated on a spot fi'om which 

 the animal could not remove them by scratching. Tlie 

 neck of a fowl, again, is another place on which large 

 numbers of a certain species have been found, collected in 

 a small area, with their lancets buried deep in the flesh. 

 They are not slow to discover when their host can furnish 

 them with no further noui'ishment, and it is curious to 

 notice how soon they abandon a dead body. This may 

 easily be observed ui the case of the cat's flea ; if a recently 

 defimct cat be watched, as the body becomes cold ajid 

 stifi", the fleas will soon be seen struggling out fi-om 

 amongst the fur, though not a single specimen may ever 

 have been seen as long as the animal was alive and warm, 

 and its blood therefore readily obtauiable. 



The human tlea is reputed to be pugnacious, and one 

 observer, who had confined a couple of females in a glass 

 tube, in order to huluce them to deposit eggs, describes 

 them as innuediately becoming " rampant, confronting one 

 another lii<e microscopic kangaroos." 



Fleas are peculiar amongst parasites as being parasitic 

 only during one stage in their career. It is only the 

 fully-grown insects by wliich we are troubled, and though 

 we find them of difl'erent sizes, little ones and big ones, 



