26 THE AMERICAN NATURALIST. [VoL. XXXVI. 
between the appendage and the median field. This portion 
may be designated the /ateral element of the sternite. Such a 
division is well shown in the abdominal sternites of the adult 
Gryllus (Fig. 14). 
More frequently, however, when a sternum in an adult 
insect is divided longitudinally it is by a single median suture, 
which perhaps represents the neural groove of the embryo. 
A sternite of a subsegment may be composed, therefore, of 
either two or three elements: in the one case the sutures 
between the median field and the lateral fields are preserved ; 
in the other, a trace of the neural groove is indicated. But 
as a rule, each sternite is an un- 
divided sclerite. 
In the same way that the posi- 
tion of the furca determines the 
line of union of the subsegments 
on the ventral aspect of a thoracic 
segment, the line of union of the 
a subsegments on the pleural aspects 
Ka: 16.— Ental surface of the pleurites is determined by the position of 
ee ts the lateral apodemes. Each of 
these is an invagination of the 
body-wall between the episternum and the epimeron. Fi ig. 16 
represents the inner surface of the pleurites of the meso- and 
metathorax of Melanoplus and shows the form of the lateral 
apodemes (af). 
For the purposes of this paper, it is not necessary to discuss 
the structure of the tergal aspect of the typical segment beyond 
a reference to the median suture, which represents the line 
of the closure of the embryo. This suture has been well pre- 
served in the head and thorax, as it is the chief line of rupture 
of the cuticle at the time of molting. 
The relations of the appendages to a typical segment are 
illustrated by the accompanying figure (Fig. 17) of the base of 
aleg of a cockroach. Near the point marked x the coxa artic- 
ulates with the ventral end of the foot of the lateral apodeme 
of the segment, Ze. with the ventral end of the episternum 
and the epimeron. This may be termed zhe pleural articulation 




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