No. 2.] LARVA OF CTENOPHORA ANGUSTIPENNIS. 557 
These serve to control the mandible, maxilla, and the labium, 
and are known as the mandibular, maxillary, and the labial 
branch. 
The brain in its finer structure is exceedingly complex. (Fig. 
47.) There are several histological elements, the various cell 
elements and the fibrillar or Punktsubstanz. The cell elements 
form the cortical portion of the brain, while the central portion 
of the brain is composed of minute granules and interlacing 
fibers. These fibers appear as cut ends in the sections, so that 
the whole medullary portion appears finely granular. In the 
cellular portion of the brain there are three distinct kinds of 
cells. There is first an outer layer of cortical cells which 
differ somewhat in size, but are always larger than the cells 
which compose the cell mass lying just within. Then there is 
the mass of rather smaller and rounded cells which lie on 
either side of the central body and extend almost around the 
brain. Among this cell mass may be seen a few very large 
cells with very darkly staining nuclei. These evidently rep- 
resent the large motor cells described by Kenyon in his work 
on the brain of the bee. The same elements may be found in 
the sub-cesophageal ganglion, although there is not so much 
definiteness in limiting the cell mass and there are fewer of the 
large cells. (Fig. 48.) There is here, in common with other 
Dipterous larvee, no sign of the complicated mushroom bodies. 
In the sub-cesophageal ganglion there is a greater amount of 
the Punktsubstanz in proportion to the size than there is in the 
supra-cesophageal ganglion. 
The thoracic and ventral ganglia show the same histological 
elements as the brain. (Figs. 49-50.) The arrangement of 
these elements is in general the same. There is an outer 
cortex layer of cells, the inner portion is composed of the cell 
mass with a few large cells interspersed, and a central portion 
which is composed of the Punktsubstanz. This arrangement 
is common to both the ventral and thoracic ganglia. Each 
nerve consists of an axis cylinder, which has a striated appear- 
ance in a longitudinal section which is due to the fine fibrillz, 
and then the enveloping membrane or neurilemma (Fig. 51). 
