NOVEMBEK 1, 1890.] 



KNOWLEDGE 



251 



accompanied by correspondinf? changes in the star's spec- 

 trum. Such may be the case, and observations in this 

 direction would probably lead to some interesting results. 



There seems to be some law governing the distribution 

 of the coloured stars. The white stars appear to be most 

 numerous, as a rule, in those constellations where bright 

 stars are most abundant, for instance, in Orion, Cassiopeia, 

 and Lyra ; yellow and orange stars in large and ill-defined 

 constellations such as Cetus, Pisces, Hydra, Virgo, &c. 

 The very reddish stars are most numerous in or near the 

 Milky Way, and one portion of the Galaxy — between 

 Aquila Lyra and Cygnus — was termed by the late Mr. 

 Birmingham " the red region in Cygnus." 



THE BED-BUG.-III. 



By E. a. Butler. 



THE eggs of the bed-bug are small, white, oval 

 objects (Fig. 11); they are laid in cracks and 

 crevices, and are caused to adhere to the surface 

 on which they are deposited by a kind of varnish 

 with which they are wet when laid. According 

 to Southall, about fifty eggs are laid in each batch. 

 The young bugs make their entry into the world by 

 pushing off a kind of lid at the end of the egg, and the 

 empty egg-shell then looks like a little round-bottomed 

 china jar with a neat rim round the opening. The 

 newly-hatched bug is a very minute, transparent, six- 

 legged creature, showing no trace of the brown colour 



which charac- 

 terizes it in adult 

 life. It is suffi- 

 ciently transpa- 

 rent to reveal 

 something of its 

 internal economy 

 through the skin ; 

 and after it has 

 had a meal of 

 blood, a dark red 

 spot appears in 

 the region of its 

 digestive appara- 

 tus. It has a 

 broad, triangular 

 head, and the antennie are short, and proportionately 

 much thicker than when full-grown. Of course, no signs 

 ot wings are apparent while the insect is in this immature 

 condition (Fig. 12). 



During the course of the larval life the skin is shed 

 several times, each moult being accompanied by a closer 

 approach to the form of the adult. The operation is 

 effected in the same way as in the cockroach, viz. by the 

 splitting of the skin along a straight line down the middle 

 of the back in the region of the thorax, and the whole 

 animal gradually extricates itself at this aperture, carefully 

 removing not merely the more robust parts of the body 

 from their covering, but neatly withdrawing also the more 

 slender parts, such as the legs and antennre, each sepa- 

 rately from its own sheath. During the moult, the claws 

 at the tips of the tarsi are useful in obtaining a foothold 

 on the irregularities of the wood, paper, &c., on which the 

 change takes place ; by this means the shells of the limbs 

 are prevented from becoming crushed and collapsed, and 

 are enabled to retain their proper forms ; hence, but for 

 the distortion caused by the I'racture along the back, and 

 the paler tint, the cast skin (Fig. 13) might easily be 

 mistaken for the insect itself. 



Fig. 11 — EuG of 

 Bed-Bug. 



.'LY-IIATCHED BuG. 



The last moult but one introduces the form usually 

 called the nj-mph (Fig. 14), which corresponds to the 

 chrysalis of those insects whose metamorphosis is com- 

 plete. As the bug grows with each moult its colour 



deepens, and its skin 

 becomes harder and 

 less flexible, so that 

 when it has reached 

 the njinph stage it 

 closely resembles the 

 adult, though still 

 rather smaller. The 

 chief differences per- 

 ceptible are in the 

 region of the hinder 

 part of the thorax and 

 the fore part of the 

 abdomen. The pro- 

 thorax is very similar 

 to that of the adult, 

 the leaf-hke margins 

 projecting b}"the sides 

 of the head ; the next 

 two segments, how- 

 ever, have not become so specialised as will ultimately 

 be their fate, and they appear as distinct bands right 

 across the body. The first of them, which is the meso- 

 thorax, already shows, however, a shght indication, at 

 the sides, of the outline of the fore ^-ings. The next 

 three segments are very similar to one another, and 

 no distinct line of division shows where the thorax ends 

 and the abdomen commences. But if we remember that 

 the thorax consists in all of only three segments, and that 

 the first of these is the very distinctly marked prothorax, 

 the determination of the line of junction of the chief 

 regions of the body becomes easy. 



While in the nymph condition the bug is stiU just as 

 active as before, and continues to take food with equal 

 readiness. At length the final moult occurs, and the in- 



13. — The Cast Skin of as Adli 

 Bug, seen from above. 



Fig. 14. — Bed-Bug at the Xvmph Stage. 



sect is sexually mature, and acquires its rudimentary 

 elytra, or upper wings. No further growth takes place, 

 as, owing to the mflexibility of the skin, this can only be 

 effected by moulting. The food now taken, therefore, 

 serves not for increase of bulk, but to maintain the proper 

 balance of the activities of the body and to supply mate- 

 rials for the perfecting and discharge of the reproductive 



