306 
Acanthia lectularia 
spiracle is not so reinforced. This diverticulum is an invagination of 
the chitin of the ventral surface, and is so immovably fastened to the 
spiracle, that prolonged boiling in caustic potash has no effect on it. In 
other Hemiptera its function is thought to be to keep water from enter¬ 
ing the trachea, as it is often found filled more or less with wax. In 
the bed bug it is empty, the creature’s manner of life being such that 
moisture will very seldom reach it, and even should it be immersed in 
water the oilj^ nature of its surface would keep it from getting wet. 
For maintaining air currents through the tracheae there are several 
sets of muscles. Joining up each segment with the next there are 
longitudinal bands on the dorsal and ventral surfaces of the bug. They 
run from the middle of one segment to the middle of the adjoining one, 
and their action, on contracting, would be to reduce the length of the 
creature and thus drive out the air. On every segment, a little to the 
inside of the spiracle and arising at the division between the bristly 
and polished portions, are other sets. These are composed of separate 
muscle bands of striped fibres, whose attachment on the ventral surface 
is confined to a circular spot, while on the dorsal surface it is lengthened 
out to a band at right angles to the length of the bug (see Plate XXIII, 
fig. 2). 
These sets are very closely surrounded by the trachea trunks, and 
have many small branches ramifying through them. Contraction of 
these muscles would tend to help expiration. There do not appear to 
be any special inspiratory muscles. 
Nervous System. 
There is not much in the nervous system of the bug which calls for 
special mention, except that it is greatly condensed. The dorsal brain 
lies immediately behind the muscles of the pharynx, and hence just at 
the border between head and thorax. At the front and sides it is 
produced forward into the thick optic lobes. Below the brain aird a 
little behind it, and thus in the pro-thorax, is found the sirb-oesophageal 
ganglion, united with the other by the commissures, which, owing to 
the dorsal brain having projecting lobes (the antennal lobes), are very 
short. Through the ring thus formed goes the oesophagus, as well as the 
two main trunk tracheae which supply the head (Fig. 26). From the sub- 
oesophageal ganglion spring the nerves of the mouth parts, and from 
it also two nerves go backwards and link up with the thoracic ganglion 
situated in the fore part of the meta-thorax, which ganglion in the bed 
