MATURATION OF UNFERTILISED EGG IN TENTHREDINID®. 573 
and in the youngest egg a group of eight chromosomes is 
seen in the polar protoplasm, with what appears to be the 
degenerating remains of another group by its side. The 
later eggs mostly show a very compact group of eight rather 
large chromosomes, which may be so regularly packed together 
that they rather resemble asmall nucleus, but have no nuclear 
membrane. Occasionally the number appears to be more 
than eight, and probably division has taken place as in 
N. ribesii. 
It is likely from these observations that the course of 
events in N. pavidus does not differ from that described in 
N. lacteus; the two inner polar nuclei probably come into 
contact and break up into chromosomes, which form two 
groups lying close together. Those in one group rapidly 
disintegrate, while those of the other remain aggregated 
together and persist for several hours. 
6. PoECcILOSOMA LUTEOLUM. 
In P. luteolum unfertilised eggs produce only females. 
The eggs are laid in little groups inside the tissue of the leaves 
of Lysimachia vulgaris, and the flies almost always choose 
for this purpose the small leaves near the apex of the plant. 
The polar mitoses take place as in N. ribesii, and result 
in four nuclei lying in a line perpendicular to the edge of the 
egg. They differ from those of N. ribesii in being nearly 
always of different sizes; the outermost is smallest, the next 
larger, and the inner or second polar nucleus largest of all, 
but not differing much from the egg-nucleus (Pl. 36, fig. 15). 
The egg-nucleus sinks very rapidly into the yolk and moves 
forward for some distance, so that it is rarely found in the 
neighbourhood of the polar nuclei; it soon begins to divide, 
and gives rise to scattered nuclei in the yolk which develop, 
as in N. ribesii. 
The second polar nucleus is generally separated from the 
others by a wider interval than in the species hitherto de- 
scribed, and the first polar nuclei are often found very close 
