36 THE AMERICAN NATURALIST. [Vor. XXXVI. 
The suture separating the postgenz from the genz is well- 
marked on the lateral aspect of the head in the Orthoptera. 
In most forms it is obsolete on the dorsal aspect but in a large 
South American cockroach that we have studied the postgenae 
are separated from the genæ and vertex throughout their entire 
extent. Upon the presence or absence of this suture on the 
dorsal wall of the head depends the presence or absence of 
the so-called occiput ; the occiput being the tergal portions of 
the postgenz (Fig. 3, O, O). 
In the ventral end of each postgena there is an acetabulum 
into which a condyle of the mandible fits (Fig. 25). Beginning 
à ——— in this acetabulum and extend- 
ing dorsad there is a suture which 
divides the postgena into two parts ; 
this suture is the more or less open 
mouth of an apodeme which extends 
into the cavity of the head. 
Here again the same relation of 
parts exists that is found in a tho- 
e racic segment. The mandible is the 
Fic. a basal segment (coxa) of an append- 
age, which articulates with the ven- 
tral ends of two sclerites (episternum and epimeron), between 
which there is a lateral apodeme. 
Thus we see that three of the head segments — the labial, 
the maxillary, and the mandibular — closely resemble a thoracic 
segment, in having on each side two sclerites, with an apodeme 
between, and an appendage below except in the case of the 
labial segment, where there has been a cephalization of the 
appendages. 
In the floor of the mouth cavity of Melanoplus there is on 
each side just behind the superlinguz a sclerite (Fig. 24, ps) 
which may represent a sternal element of the mandibular seg- 
ment. The position of this sclerite farther in the mouth cavity 
than the superlinguz is that which would be occupied by a 
mandibular sternite, as such a sternite must precede the super- 
linguæ in the course of the invagination of the mouth; equally 
suggestive is the fact that this sclerite is closely connected 

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