No. 421.] SKELETON. OF THE HEAD OF INSECTS. 33 
cervical sclerite is the episternum of the labial segment, and 
the posterior one the epimeron. This conclusion is confirmed 
by the fact that the posterior of the two lateral cervical scle- 
rites articulates with the episternum of 
the prothorax, and the anterior one with 
what we believe to be the epimeron of 
the maxillary segment. 
The ventral cervical sclerites in this 
order are either two in number, Peri- br 
planeta (Fig. 21), or constitute two trans- 5... — Vental und asc 
verse series, Stenopelmatus (Fig. 22), cervical sclerites of Peri- 
Gryllus (Fig. 23). We regard these as He 
constituting the sternites of the two subsegments of the labial 
segment. If this view be correct, the anterior sclerite or series 
: of sclerites represents the sternum of 
the labial segment, and the posterior 
the sternellum. The division of a 
sternite into a transverse series of 
either two or three sclerites is com- 
parable with what frequently takes 
place in the sternites of the thorax 
and of the abdomen, already discussed 
on an earlier page. 
The appendages of this segment, the 
ime E —-j] second maxillae, project forwards from 
Fic, 22. — Head of Stenopelma- the front margin of the segment as a 
5n i single organ, the labium. This anoma- 
lous condition is the result of a migration of the appendages 
forwards and towards each other and of a coalescence, which 
has been figured by many writers and 
often described, lately in detail by 
Deegener (00). As a result of this 
coalescence the united cardines be- 
come the submentum, and the stipites ; | 
the mentum. Fic. 23. — Ventral cervical sclerites 
2 of Gryllus. 
In the more generalized insects a 
gula is not developed as such. We have devoted much study 
to the question of the homology of the gula and conclude that - 

3 












