466 THE NERVOUS SYSTEM. 
this nerve-root (Pl. XXIX., Fig. 2). There is a distinct analogy 
between these decussating tracts and the anterior pyramids 
of the medulla oblongata of Vertebrates. 
The Maxillary Nerves.—This pair of nerves arise from the 
lowest part of the infra-cesophageal ganglia. They are the 
great nerves of the proboscis, and supply all its structures 
except the pharynx. The fact that only a single pair of nerves 
supplies the proboscis is in favour of the view that it consists of 
only a single pair of metameral appendages. The question 
may arise: why should these nerves be termed maxillary 
rather than labial ? 
In answer it may be remarked that there is a tendency to- 
wards the reduction of the size of the labial, and an increase 
in that of the maxillary nerves, as we advance from the less to 
the more highly-specialised Insecta. I know no insects which 
exhibit the reverse condition. This would not, perhaps, be a 
cogent argument taken by itself, but it is worthy of note in 
relation to my contention that the proboscis is developed from 
the maxille of the embryo. 
The Ganglia of the Crura (Pl. XXX., Fig 3, g cv).—These con- 
sist of two distinct lobes in front of the crura, which are 
covered by a thick layer of nerve cells, occupying the sulcus 
between the antennal and infra-cesophageal ganglia. They give 
origin to the pharyngeal nerves, and probably represent the 
ganglia of the antenne of the Crayfish, from which the pharyn- 
geal and antennal nerves arise in close proximity to each other. 
Gaskell has compared the ganglion of the crus with the locus 
niger of the Vertebrate, but it appears to me that evidence is 
wanting to justify such a comparison. 
The Pharyngeal Nerves arise from the crura between the infra- 
cesophageal and the antennal ganglia by two roots, and from 
the large superficial cells of the ganglion of the crus, which lie 
in the sulcus between the antennal and infra-cesophageal 
centres. These nerves are far smaller than the maxillary, and 
are distributed to the pharyngeal muscles. 
The Pyramidal Ganglion.—This is a large pyramidal group of 
nerve cells, many of which are distinctily stellate. It is 
