28 THE AMERICAN NATURALIST [Vor. XXXVI. 
this inverted Y-shaped suture are those developed from the 
procephalon, while the stem of the Y represents the line of 
union of the cephalic lobes. 
When we take into account the position of the mouth (see 
Fig. 11), it is evident that the parts developed from the pro- 
cephalon pertain to the ventral aspect of the body. In the 
course of development there is a dorsal flexure of the cephalic 
region by which the preoral sterna are bent up towards the 
tergal aspect (Huxley, '78, p. 343); this has been described by 
several observers (see Korschelt and Heider, '99b, p. 302). 
As a result of this dorsal flexure, the former most anterior 
part of the procephalon assumes a more backward position, 
which led to the part derived from it being termed by Newport 
the clypeus posterior. As this term is morphologically incor- 
rect, we have adopted the name front for this part, and restrict 
the term c/ypeus to the clypeus anterior of Newport. 
It seems obvious that the three sclerites derived from the 
procephalon, — the front, the clypeus, and the labrum, — rep- 
resent the sternites of the three preoral segments.. 
As to the front, it bears the median ocellus, and, in the 
Plecoptera, the paired ocelli also ; and as the ocelli are inner- 
vated by the protocerebrum, it is evident that the dere is a 
part of the protocerebral segment. 
In this connection reference should be made to a migration 
of the paired ocelli. The condition in the Plecoptera, where 
the front bears all the ocelli, is probably the most generalized ; 
for in this order, as will be shown later, the most nearly primi- 
tive position of the antennz is found; and, too, in this order 
the most generalized condition of the tracheation of the wings 
exists (Comstock and Needham, '98, p. 237). In the Orthoptera 
(Blattidae and Gryllidae) the paired ocelli are in the suture 
between the front and the vertex. In certain Ephemerida the 
paired ocelli are in this suture, while in others they have passed 
on into the vertex. In the more specialized orders, wherever 
we have been able to distinguish between the front and the 
vertex, we have found the paired ocelli in the vertex. 
The labrum is innervated by the tritocerebrum ; for this 
-~ reason we — s it as the sternite of the tritocerebral segment, 


