40 THE CLASS OF INSECTS. 



full-grown caterpillar ; we haA-e counted about sixty a minute 

 in the recentlj- hatched larva of Diplax. During excitement, 

 the number of pulsations increases in rapidity. Newport found 

 the pulsations in a bee, Anthopliora., when quiet, to be eighty a 

 minute ; but when " the 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." 



He found that the number of pulsations decreased after each 

 moult of the larva of Sphinx ligustri, but 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 twehe, and, during the 

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

 fect insect it rose from fort^'-one to fifty, and Avhen excited by 

 flight around the room it Avas from one hundred and ten to one 

 hundred and thirty-nine." 



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

 they live in the Avater, respire, by means of branchite, the 

 air mixed mechanically with Avater. Respiration is carried on 

 by an intricate sj'stem of tubes (pul- 

 monary trachete) Avhich open by pores 

 (spiracles or stigmata) in the sides of 

 the body ; or, as in aquatic insects, by 

 branchia2, or gill-like flattened expan- 

 sions of the body-Avall penetrated by 

 tracheae (branchial tracheae). 



There are normally eleven spiracles, 



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



of the bod}' ; each consisting of an oval 



horny ring situated in the peritreme 



^ig-is. and closed by a valve, which guards 



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



within by another valve Avhich covers the entrance into the 



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



Fig. 48. Larva of the Humble-bee just beginning to change to a pupa, showing 

 eleven pairs of stigmata. In the adult bee, only the third pair is apparent, the 

 remaining pairs being concealed from view, or in part aborted. In most insects 

 ;tbere are usually only nine pairs of stigmata. — Original. 



