Tue Biotocy or ErHypRA SUBOPACA LOEW 573 
the posterior half of the central ganglion arise three unpaired accessory 
nerves which are much finer than the others. Except in the first four 
branches (I, II, a, and b) the bifurcations of these nerves are very similar 
to that in the Musca larva, while in innervation there is practically no 
difference between these two forms (Plate LV, 13). Each of the fourteen 
paired nerve branches is associated with a trachea (Plate LIV, 10). The 
penetration through the ganglionic sheath’by the trachea gives a metallic 
luster along the edge of the ganglion. 
There are two prominent pairs of sense organs in the head region. 
The anterior pair is on the antennae and the posterior pair is on the maxil- 
lary palpi (Plate LIV, 2). The palpi are shorter than the antennae, are 
not jointed, and have a broader base. The innervation of the former 
comes from the subesophageal ganglion (Tragardh), that of the latter 
from the cephalopharyngeal mass. On the dorsal and lateral parts 
of the thorax, and along the lateral of the entire abdomen, parallel to the 
main tracheal trunks are papillae of another type which are much more 
slender, with a cylindrical stem. At the tip of the stem branch are three 
or four tentacles. These have been figured by Tragardh (1903). The 
nerve ganglia lie close above the upper pharyngeal plate. They are 
fused anteriorly but clearly separated from each other behind. These are 
the epipharyngeal ganglia. Just opposite to them, on the ventral side 
of the pharynx, are the hypopharyngeal ganglia. These two pairs are 
best seen in cross sections. 
The muscular system— The muscles, aside from those of the alimentary 
and vascular tracts, are in two main groups—one controliing the cepha- 
lopharyngeal region, the other constituting a part of the body wall. It 
is these two main groups of muscles which are herein discussed. 
The cephalopharyngeal muscles— In the cephalopharyngeal region the 
muscles are very similar to those found in the larva of Musca. Starting 
from the cephalic end, a pair of mandibular extensors is seen, inserted 
on the dorsal side of the mandibular sclerites. The attachment of these 
muscles is made to the dorsal body wall of the third segment. Caudad 
to these another pair of muscles is inserted on the dental sclerites. These 
are the mandibular depressors. The other end of this pair on each side 
is divided into three bands and attached to the ventral process of the 
lateral pharyngeal plate. On the hypostomal sclerites are inserted four 
pairs of muscles, two dorsal and two ventral. The dorsal pairs are attached 
