No.421.] SKELETON OF THE HEAD OF INSECTS. 21 
the pair immediately in front of the maxillary ganglia were 
the mandibular ganglia (see Korschelt and Heider, '99b, p. 326); 
but it is more probable that the first of these four pairs of gan- 
glia (Fig. 10, 7) pertains to the man- 
dibular segment and that the second 
pair are the homologues of the super- 
lingual ganglia figured by Folsom. 
The seven segments of the head 
are designated as follows: 

First, ocular, or protocerebral. 
Second, antennal, or deutocerebral. 
Third, second antennal, or tritocerebral. 
Fourth, mandibular. 
Fifth, superlingual. 
Sixth, maxillary. Fic. ro. — Head of embryo of 
Seventh, labial, or second maxillary. Acilius, after Patten. 




DIAGRAMS OF THE ELEMENTS OF THE HEAD. 
The head of an insect consists of seven segments closely 
consolidated, greatly reduced in length, and, in the case of 
some, bent out of the original line. The morphological rela- 
tions of these segments can be shown by representing them 
as distinct, of uniform size, and in a direct line. This is done 
in the accompanying diagram (Fig. 11, A). 
Let us trace the steps by which this diagram was made. 
First, the outlines of the seven segments were drawn as if no 



Fic. 11.— Diagrams of the elements of the head: A, lateral aspect; B, ventral aspect. 
reduction or consolidation of any of them had occurred; at 
this stage the diagram might represent the cephalic end of 
an earthworm, except that the prostomium is not represented. 
