22 THE AMERICAN NATURALIST. [Vor. XXXVI. 
Second, a longitudinal line was drawn representing the line 
of separation of the sternal from the pleural elements of the 
segments ; it is along this line that the appendages are borne. 
Third, the chain of ganglia were added, a pair of ganglia in 
each segment; -as the nervous system is developed from the 
ectoderm on the ventral side of the body between the append- 
ages, it is represented in the sternal portion of the preoral 
segments as well as in the postoral segments. The diagram 
being of a side view, only a single member of each pair of 
ganglia and longitudinal commissures are shown. Fig. 11, B, 
is a diagrammatic representation of a ventral view of the 
nervous system. Fourth, the compound eyes and the ocelli 
were represented in the first segment (Fig. 11, A), because 
they are innervated by the protocerebrum. The reasons for 
the exact positions within the segment assigned to these 
organs will be discussed later. Fifth, the position of the 
appendages was indicated, a pair to each segment except the 
first. It will be remembered that the antennz are innervated 
by the deutocerebrum; hence they pertain to the second seg- 
ment. Sixth, the mouth was represented as opening in the 
ventral wall of the third segment; this is in accordance with 
the results of the studies of Viallanes (87a), who has shown 
that, although the third pair of ganglia enter into the com- 
position of the supra-cesophageal ganglion, the commissure 
- Which connects them passes behind the cesophagus. This is 
shown in the second diagram. Although the position assigned 
to the mouth in these diagrams was suggested by the results 
of the studies of Viallanes, it is not in accordance with his 
conclusions; for he evidently believes that the mouth opens 
between the third and fourth segments. Our view is based 
on the well-known fact that the mouth of the embryo is 
formed zz the labrdl rudiment and not behind it. 
The determination of the position of the mouth is one of the 
most striking of the results of the later studies of the head. 
Naturally the older entomologists believed that the mouth- 
opening was at the cephalic end of the body, and this effectually 
onites; trois sont prebuccaux et trois 
Peet = whe oS im : £. 

| post-buccaux." — Villanes (87b, p- 117). 
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