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3 T. crepuscularia (biundularia). The first two sets showed 
considerable differences, which were exhibited by drawings 
made under the microscope by Messrs. Rowe and Baty. The 
eges of T. bistortata, as exemplified by the batch that had 
been examined, were long and cylindrical with rounded 
ends. Those of T. crepuscularia (biundularia) were of only 
from half to two thirds the cubical contents of those of 7. 
bistortata, and although exhibiting considerable variation 
were of a somewhat oval form, or inclining to the shape of 
a hen’s egg. To the naked eye there did not appear to be 
much difference in colour, both being a pea-green, but those ~ 
of T. crepuscularia (biundularia) were of a somewhat yellower 
tint. Under the microscope, however, the difference>of 
colour became more marked, that of 7. bistortata appearing 
of a pearly-green hue, those of T. crepuscularia being yellow ; 
and whilst the shell of the former was iridescent and slightly 
transparent, the latter was somewhat opaque. There were 
also faint traces of longitudinal ribbing just round the 
shoulder of the micropylar end in the egg of T. bistortata, 
such traces not being discernible in the egg of T. crepus- 
cularia. The egg of T. bistortata, too, was also noticeable 
for small irregular depressions which occurred on the 
surface, and which appeared to be due to the contraction of 
the protoplasmic contents of the egg. These were not to 
be seen in the egg of T. crepuscularia, the shell of which 
appeared under a high power to be minutely pitted. Another 
character of differentiation in the two sets of eggs observed 
was in the position of the lateral depression which is so 
characteristic of many Geometrid eggs. In the egg of T. 
bistortata the depression was placed well toward the micro- 
pylar end, whilst in the egg of T. crepuscularia it 1s placed 
much nearer to the centre. 
In the set of T. bistortata eggs examined, which had been 
fertilised by a male T. biundularia, the general shape, colour, 
and appearance were very similar to those of the first set of 
T. bistortata. The eggs were, however, slightly smaller, and 
tended to be a little more rounded at one end than the other, 
showing some trifling variation between the two sets, and 
one or two of the eggs out of a considerable number exa- 
mined exhibited a most complete oval shape. They were, 
however, still very distinctly T. bistortata eggs, as apart from 
those of T. crepuscularia. In colour the cross-fertilisation 
seems to have had some effect, for the eggs were, under a 
good power, certainly yellower than the other batch of T. 
bistortata eggs. This may, however, have been due to a 
