40 THE CLASS OK INSECTS. 



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

 in ihc recently hatched larva of J)ij>/ti.r. During excitement, 

 the number of pulsations increases in rapidity. Newport found 



tin- pulsations in a bet 1 , ^iiitli<t/>li<>r<i. wlii'ii quiet, to lie eighty a 

 minute ; but when "the inserts wore 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 iittiiilicr of pulsations decreased after eaeli 

 moult of the larva of >'/</////..; lii/nnfri. but inereased 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 around the room it was from one hundred and ten to one 

 hundred and thirl v-niue." 



<)i;<..\\> OF IvKM'iK.vrioN. All insects breathe air. or, when 

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

 air mixed mechanically with water. Respiration is earned on 



by an intricate system of tubes (pul- 

 monary trachea-) which open by pores 

 (spiracles or stigmata) in the sides of 

 the liodv: or. as in aquatic insects, by 

 branchia 1 , or gill-like flattened expan- 

 sions of the body-wall penetrated by 

 trachea.- (branchial trachea'). 



There are normally eleven spiracles, 

 or breathing-holes (Fig. 4$), on each side 

 of the body; each consisting of an oval 

 horny ring situated in the poritreme 

 F 'fe r - 4S - and closed by a valve, which guards 



the orifice (Fig. 4U). Within this valve is a chamber closed 

 within by another valve which covers the entrance into the 

 trachea'. The air-tube itself (Fig. ;"><)) consists of "au external 



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

 eleven pairs of stigmata. In the ailult 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. 



