/ 



40 THE CLASS OF INSECTS. 



full-gi-own caterpillar ; -we have counted about sixt}' a miDUte 

 in the recently- hatched larva of Diplax. During exciteisent, 

 the number of })ulsations increases in rapidity. Newport Ajund 

 the pulsations in a bee, Antliophora, Avhen quiet, to Ite e^hty a 

 minute ; but when "the insects were quite lively, and liad 1)eeu 

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

 tions amounted to one hundred and forty." 



He found that the number of pulsations decreased after each 

 moult of the larva of Sphbix ligustri, but increas/d in force; 

 when it was full grown and had ceased feeding /t 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 entirel}^ ceases ; but in the per- 

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

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

 hunclred and thirty-nine." / 



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

 the}^ live in the water, respire, b}^ means of branchiae, the 

 air mixed mechanicall}^ with water. Eespiration 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 

 branchiiE, or gill-like flattened expan- 

 sions of the body-wall penetrated by 

 tracheoe (branchial trachepe). 



There are sometimes eleven spiracles, 



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



of the body ; each consisting of an oval 



horn}^ ring situated in the peritreme 



Fig- 48. a,nd closed by a valve, which giiards 



the orifice (Fig. 49). Within this A'alve 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. 4S. Larva of the Humble-bee just beginning to change to a pupa, .showing 

 eleven pairs of stigmata. In the adult bee, only the foiirth 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. 



