40 THE CLASS OF INSECTS. 



full-grown caterpillar ; we have counted aliout sixty a minute 

 in the recentl}' hatched larva of Diplax. During excitement, 

 the number of pulsations increases in rapidity. Newport found 

 tlie pulsations in a bee, Anthox)hora, when quiet, to be eighty a 

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

 exposed to the sun for an hour or two, the number of pulsa- 

 tions amounted to one hundred and forty." 



lie found that the nnmhcr of pulsations decreased after each 

 moult of the larva of ^SjJ'nix h'tjustri, l)ut increased in force; 

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

 "After it had passed into 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 

 flight arouml the room it was from one hundred and ten to one 

 hnndred and thirty-nine." 



Organs of Respiration. All insects breathe air, or, when 

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

 air mixed mechanically with water. Respiration is carried on 

 by an intricate system of tubes (pul- 

 monary trachete) which open by pores 

 (spiracles or stigmata) in the sides of 

 the body ; or, as in aquatic insects, by 

 branchiae, or gill-like flattened expan- 

 sions of the body-wall penetrated by 

 trachea? (branchial tracheie). 



There are normally eleven spiracles, 



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



of the body ; each consisting of an oval 



horny ring situated in the peritreme 



Fig. 48. and closed by a valve, which guards 



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



within b}' another valve which covers the entrance into the 



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



Fig. 48. Larva of the Hnmble-hee just beginning to change to a pupa, showing ten 

 pairs of stigm.Tta In the adult bee, only the third pair is apparent, the remaining pairs 

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

 nine pairs of stigmata. — Original. 



