THE DEVELOPMENT OF THE NERVOUS SYSTEM. 491 
is exceedingly complex. Not only is the central stroma divided 
into distinct lobes even in the recently-hatched larva, but the 
two great commissures, one below and the other above the 
cesophagus, are already developed. In the adult larva the 
optic ganglion is not only recognisable, but its central stroma 
already exhibits the radial and concentric structures so charac- 
teristic of the same part in the imago, and the cells of the 
pyramidal ganglion and of the olfactory ganglia are readily 
distinguished. In Plate III. two sections of the brain of the 
larva are represented at a somewhat more advanced stage of 
development than those which are now published. In Fig. I. 
the section is entirely behind the optic ganglion, and exhibits 
the trabeculae and corpora fungiformia ; and in Fig. II. it is in 
front of the optic ganglion, and shows the two cesophageal 
commissures. In several of the sections in the series from 
which these two figures are taken, the optic ganglia are dis- 
tinctly recognisable ; but owing to these sections having been 
broken, they were not figured, and the appearances which they 
presented puzzled me much at the time, as I was then un- 
acquainted with the manner in which the optic ganglia are 
embedded in the substance of the hemispheres. 
Changes of the Neuroblast in the Pronymph.—The first change 
which attracts our attention in the neuroblast in the early 
stages of pupation is the rapid increase in the size of the hemi- 
spheres. This is accompanied by a similar increase in the 
rudiments of the infra-cesophageal ganglia, which become 
segmented from the anterior part of the ventral cone; and by 
a rapid increase in the size of the cesophageal connectives. 
The hemispheres at the same time become ovoid, with their 
long axes transverse to the body. This elongation is due to 
the rapid increase in the size of the optie ganglia, which pro- 
ject more and more from the surface of the hemispheres. 
Weismann [2], describing the changes which occur on the 
third day of the pupa, states that: ‘ Each hemisphere, which 
during the first two days underwent an extraordinary enlarge- 
ment, exhibits a moderately-deep circular groove on its surface, 
separating a median from a lateral ganglion. These both 
