40 THE CLASS OF INSECTS. 



full-grown caterpillar ; wc have counted about sixty a minute 

 in the recently hatched larva of Dipic'x- During excitement, 

 the number of pulsations increases in rapidit3\ Newport found 

 the pulsations in a bee, Antho]}1iora^ Avhen quiet, to bo eighty a 

 minute ; but when "the insects were quite lively, and had been 

 exi)0sed to the sun for an hour or two, the number of pulsa- 

 tions amounted to one hundred and forty." 



He found that the nmnher of pulsations decreased after each 

 moult of the larva of ^SpJ^^vx lirjustri., but increased in force; 

 when it was full grown and had ceased feeding it was thirty. 

 "After it had passed int(j the pupa state the number fell to 

 twenty-two, and afterwards to ten or twelve, and, during the 

 period of hibernation, it almost entirely ceases ; but in the per- 

 fect insect it rose from forty-one to fifty, and when excited by 

 (light around tl:c room it was from one hundred and ten to one 

 iumdrcd and thirty-nine." 



Orgaxs of EEsriRATiox. All insects breathe air, or, when 

 they live in the water, respire, by means of branchiae, the 

 ah- mixed mechanically with water. Respiration is carried on 

 l)y an intricate system of tubes (pul- 

 monary trachejc) which open by pores 

 (spiracles or stigmata) in the sides of 

 the body ; or, as in aquatic insects, by 

 branchite, or gill-like Hattened expan- 

 sions of the body-wall penetrated by 

 tracheae (branchial trachete). 



There are normally eleven spiracles, 



or breathing-holes (Fig. 48), on each side 



of the body ; each consisting of an oA'al 



horny ring situated in the peritreme 



^'s-48. {1,1(1 closed by a valve, which guards 



the orifice (Fig. 49). Within this valve is a chamber closed 



within by another valve which covers the entrance into the 



tracheae. The air-tube itself (Fig. 50) consists of "an external 



Fig. 48. Larva of (he Hnmblc-beejupt beginning to change to a pnpa, showing ten 

 pairs of Ktigm.ita In the adult boo, only the third pair is apparent, the remaininc pairs 

 being concealed from view, or in part aborted. In most insects there are usually only 

 nine pairs of stigmata. — Onginal. 



