206 
Psyche 
[Aug.-Oct. 
sal plate of tergite t with a lateral subtergite or pleurite pi on 
each side (probably a demarked portion of the tergite proper), 
and a sternite or ventral plate s seperated from the subtergites 
by a lateral membrane. The spiracles sp are borne at the anterior 
ends of the subtergites pi, and if the first segment can be taken as 
the criterion, the spiracles apparently belong to the antero-lateral 
area of the tergite which becomes detached to form the subtergite 
The membranes connecting successive segments are called con- 
junctiva, and this term is also applied to the membrane connect- 
ing the sclerites of the abdominal segments. It is preferable to 
distinguish the lateral membranes, however, and they are here 
referred to as the lateral or pleural membranes. 
The spiracles are extremely interesting structures, and the first 
may be taken as an illustration of the way in which a closing ap- 
pliance was developed to prevent the entrance of deleterious 
substances. If the first spiracle sp (counting from the base of the 
abdomen) of Fig. 14 is removed with its surrounding body wall, 
and is examined from within, after removing the soft parts, it 
may readily be seen that within the atrium or entrance chamber 
there is a triangular sclerite of suboperculum sop of Fig. 19, 
which was located ventrally when the spiracle was in situ, as 
in Fig. 14, but is apparently dorsal in Fig. 18, which depicts the 
inner surface when the fragment containing the spiracle is turned 
over and viewed from within. Certain occlusor muscles such as 
the one labelled m in Fig. 18 are attached to the suboperculum 
sop and extend to the arch or bow sar called the spirarcus. 
When these occlusor muscles contract, the bow sar, which pivots 
at the point p, is drawn up against the suboperculum sop and 
effectively closes the entrance to the trachea by pinching the 
tube together. When the occlusor muscles relax, the elasticity 
of the parts cause them to spring back, and the trachea is opened 
again. This is but one more of the marvellous little mechanical 
devices developed by these interesting creatures, and as one studies 
their anatomy one’s wonder increases that Nature has endowed 
them with such cleverly efficient mechanisms for carrying on the 
commonplaces of a cockroach’s existence — though I suppose we 
should naturally expect to find some pretty efficient devices in 
an organism which has successfully maintained itself for so many 
