The Structure and Special Physiology of Insects 1 9 



on it not merely to take up oxgyen from the outer air and give up the 



waste carbon dioxide of the 

 body, but also to convey these 

 gases to and from all the tis- 

 sues of the body. The blood 

 is not red, but pale yellowish 

 or greenish, and is really more 

 like the lymph of the ver- 

 tebrate body than like its 

 blood 



Insects do not breathe 

 through the mouth or any 

 openings on the head, but have 

 a varying number (usually 

 from two to ten pairs) of 

 small paired openings on the 

 FlG - 37- FIG. 38. sides of the thorax and abdo- 



FIG. 37. Diagram showing respiratory system of pupa men. These openings, called 

 of mealy-winged fly, Aleyrodes sp.; only two pairs --.-.^j-. or stmmata are ar 

 of spiracles are present. (After Bemis; much spiracles, O. Stigmata, are ar- 

 enlarged.) ranged segmentally and in 



Fl ^3 8 .-Diagram of t] if heae S hea , d f c c !l roach - most insects are to be found 

 Note branches to all mouth-parts, and the an- 

 tennae. /., tracheae, or air-tubes. (After Miall on two of the thoracic seg- 

 and Denny.) ments an( j on a u tne abdomi- 



nal segments except the last two or three. The openings are guarded by fine 

 hairs or even little valvular lids to prevent 

 the ingress of dust, and are the entrances to 

 an extended system of delicate air-tubes or 

 tracheae which branch and subdivide until 

 the whole of the internal body is reached 

 and ramified by fine capillary vessels bring- 

 ing fresh air to all the tissues and carrying 

 off the waste carbon dioxide made by the 

 metabolism of these tissues. The usual 

 general arrangement of this elaborate re- 

 spiratory system is shown in Figs. 34, 35, 

 and 36. Short broad trunks lead from 

 each spiracle to a main longitudinal trunk 

 on each side of the body, from which 

 numerous branches arise, these going to 

 particular regions of the body (Fig. 38) FIG. 39. Piece of trachea (air-tube), 



and there branching repeatedly until S reatl J ma g n .i fi . e d> showing spiral 

 .... , / thread (taemdia). (Photomicro- 



even individual cells get special tiny graph by George O. Mitchell.) 



