APHANIPTERA FLEAS 



523 



We all know that the Flea is so flat, or compressed sideways, that it 

 does not mind the most severe 

 squeeze. This condition is 

 almost peculiar to it ; a great 

 flattening of the body is com- 

 mon in Insects — as is seen in 

 another annoying Insect, the 

 bed-bug — but the compression, 

 in the flea, is in the reverse 



direction. In other respects the Fig. 2bO.—Hystrichopsyna talpae. Britain. 

 , , , c ,\ a (After Ritsema. ) 



external anatomy 01 the flea 



shows several peculiarities, the morphological import of which has 

 not yet been elucidated. The head is of very 

 peculiar shape, small, with the antennae placed 

 in an unusual position ; the clypeus is said to 

 be entirely absent, the front legs are articulated 

 in such a manner that they have a large addi- 

 tional basal piece — called by some anatomists 

 the ischium — and in consequence appear to be 

 placed far forwards, looking as if they were 

 attached to the head ; the meso- and meta- 

 thorax have certain flaps that have been con- 

 sidered to be homologues of wings ; and the 

 maxillary palpi are attached to the head in 

 such a way that they appear to play the part 

 of the antennae of other Insects (Fig, 250), 

 and were actually considered to be the antennae 

 by Linnaeus, as well as others ; the mouth- 

 parts themselves are differently constructed 



The maxillae 



Mi Lu 



Fig. 251. — Mouth 

 parts of a flea, Yer 



mipsylla aiakurt from thosc of any other Insects.^ 



pricking organ ; and labium are considered to be not only present, 



Lp. labial palp ; i^^j^ ^^Q\\ developed, the former possessing palpi 



Md. mandible; . , ,i n , -, f -i , T , • , 



iMx.m&xiWa. ;Mxp. moderately well developed, while the labial 



maxiUaiy ^ palp, p^ipg .j^^.g very large and of highly peculiar 



form, being imperfectly transversely jointed 



and acting as sheaths ; the mandibles are present in the form of 



^ The best general description of the external anatomy of the flea is to be found 

 in Taschenberg, Die Flohe, 1880. The morphology is better elucidated, though still 

 incompletely, in Wagner's valuable " Aphanipterologische Studien," Rorae Soc. ent. 

 Moss, xxiii. 1889, pp. 199-260, 5 plates, and op. eit. xxxi. 1897, pp. 555-594, 3 

 plates. Cf. also K C. Rothschild, Xov. Zool. v. 1898, pp. 5-33-54-4, 3 plates. 



