DEVELOPMENT OF TH1CHOGRAMMA EVANESCENS. 165 
of the nucleoplasmie zone. This process may go on till the 
nucleus becomes normal, that is, until a rough reticulum is 
produced, and sometimes the chromatin becomes very sparse. 
These changes are shown in PI. 12, figs. 40-43. In PL 11, 
fig. 15 such nuclei are marked N., and in PL 11, fig. 25, there 
is a large group of them towards the centre of the embryo. 
I do not know the reason for this reversion to the usual 
chromatic arrangement, but at a much later stage during 
pupation the early abnormal form of nucleus gives place to 
the normal one. The nervous system of the larva, for instance*, 
is formed of nuclei having quite a different chromatic 
arrangement from that of the adult. I feel convinced that the 
curious form of nucleus found in the larva is connected with 
the unusual metabolic conditions to which the developing egg 
is exposed. Inspection of PL 11, fig. 15, will show that a 
large number of nuclei are sinking inwards, but among them 
the nuclei marked N.S.I., which are the original endoderm, 
are remarkable for their size. In this figure the extruded 
nuclei and the inner mass of the egg have been thrown out on 
the mid-dorsal side, and lie in the space formed by the gas- 
trulating periphery of the ovum ( INV .). The germ cells lie 
towards the ventral edge of the posterior pole of the egg 
and have sunk inwards ; at Z. the edge of the blastodernl 
tends to embrace the pocket in which the germ cells lie. 
The latter stain very faintly, and form a light area on the 
posterior pole of the egg. Fig. 23 of PL 11 is a transverse 
section through this part of the egg, near the letters A -A ill 
PL 11, fig. 15. The latter figure is a little earlier than the 
former. In PI. 11, fig. 22, drawn at twice the magnification 
of either PL 11, figs. 9 or 23, is an oblique longitudinal sec- 
tion of the posterior pole of the egg to show both the manner 
in which the germ cells sink into the egg in the form of a 
pocket (G-CP.), the neighbouring blastoderm nuclei ( X.X .) 
surrounding and protecting the pocket, and the relative 
staining power of the egg cytoplasm and the germ cell cyto- 
plasm. Up to the stage drawn in Fig. 15 of PL 11, the 
somatic nuclei of the egg are scattered in a syncytium ; in 
