202 W. H. FURLONGE ON THE PULEX IRRITANS. 



protruded considerably, and sometimes being retracted beneath the 

 margin of the excavation in the terminal plate. The soft spongy 

 mass, of which the organ appears to be composed, is perforated by 

 a variable number of circular orifices, from 24 to 28 in number, 

 between which the surface is thickly studded with very short, 

 brown, spinous hairs. These orifices open into hemispherical cavi- 

 ties, around the margin of each being inserted a flat, chitinous ring 

 (see Fig. 2), from which about ten or twelve flattened bands or 

 spokes, of the same width, radiate towards the centre for about half 

 the radius, altogether constituting a flat disc, the inner margin of 

 which appears dentated, (except under very high powers), from the 

 projection of the flat bands or spokes ; From the bottom of each 

 cup-shaped cavity, arises a fleshy cone, the apex of which is in the 

 centre of the discoid ring, and from it emerges along, fine, straight, 

 single hair of great flexibility.* These hairs collectively constitute 

 a tuft or brush of singular beauty, the hairs standing nearly up- 

 right, or inclining slightly outwards. 



When a young and transparent specimen, — of which the large 

 intestinal sac is well filled with blood, — is gently compressed and 

 examined by light reflected from a side parabolic illuminator, 

 numerous thread-like tracheal tubes, (see Fig. 4) may be seen most 

 distinctly, proceeding from the under surface of the pygidium, (pre- 

 sumably from the orifices therein), and uniting together into several 

 larger tubes which join the upper main tracheae of the insect. It 

 is very interesting to watch the constant movements of the pygi- 

 dium, upwards, downwards, and laterally, and the consequent waving 

 motion of the white thread-like vessels proceeding from it, pro- 

 jected upon the dark back ground of the intestinal sac behind, 

 which owing to the transparency of the chitinous envelope, can be 

 seen most clearly. 



There has been, and still exists, considerable diversity of opinion 

 as to the use or purpose of this very curious organ. By some it 

 has been supposed to be connected with the respiratory system, by 

 others it is suspected that it fulfils some undiscovered office in the 

 reproductive functions of the insect, — while the more cautious 

 observers contend that, as yet, we possess no knowledge whatever on 

 the subject. T certainly am not in a position to solve the problem, 

 though I frankly confess that — having reference to the very 



* The ideal section of one of the orifices shewn in fig. 3 explains my idea of 

 the structure I have described. 



