INTERNAL STRUCTURE. 



25 



The Respiratory System. The air is distributed through the 

 system by tracheae or air tubes ; these open at the stigmata or 

 spiracles. Ten pairs of spiracles are present, eight of which occur 

 on the eight basal abdominal segments, and, as we have seen, a 

 pair each on the meso- and metathorax. Janet has described and 

 figured elaborate valves with which the stigmatic orifices are 

 furnished. 



The Muscular System. The only point that concerns us here is 

 the interesting fact, demonstrated by Janet, that the wing-muscles 

 in queen ants after the marriage flight become degenerated through 



Pedunculate body 



Maxillary 

 glands 



Cribellum 



Mandibular 

 glands 



Ducts 



Cribellum 



Reservoir of 



mandibular 



glands 



Buccal cavity 

 Fig. 42. Brain, etc., of Donisthorpeafuliginosa'Q. (Crawley.) 



histolysis. The fatty and albuminoid substances thus derived are 

 carried to the abdomen in the blood, where they are taken up by 

 the ovaries and assist the growth of the eggs. When the greater 

 part of the wing-muscles has disappeared the thoracic tracheae 

 become considerably enlarged, in consequence of which old queens 

 will float when placed in water, etc. 



The Nervous System. Ganglia occur in the head, pro-, meso-, 

 and metathorax, and abdomen. These are connected by two 

 longitudinal cords, and nerves run from the ganglia to the various 

 organs. The ganglion above the oesophagus is considered to be the 

 brain. The frontal lobes of an ant's brain, which have been com- 

 pared with the cerebrum of vertebrates, contain two pairs of pedun- 

 culate, or mushroom bodies, the corpora pedunculata. The olfactory 



