]\IE. LUBBOCK ON THE OVA AND PSEUDOVA OE INSECTS. 363 
these oval green cells in a specimen which still contained the three vitelligenons cells 
unaltered, but believe that I have done so in a few instances. 
These parasitic cells are present in such great numbers in the full-grown female, that 
there is no difficulty in accounting for the entry of some of them into the egg ; but it is 
difficult to understand why they do not appear in other parts of the egg-follicle, and why 
they increase so rapidly at a particular period in the development of the egg. 
Weak solutions of oxalic acid, of tartaric acid, and of sulphuric ether produced no 
effect upon these cells. 
The mature egg, besides the oil-globules and the surrounding fluid, contains also 
numerous vitelline spherules, which have every appearance of being true cells, but that 
they contain no nucleus. 
I have sometimes found a few of these spherules (or others very nearly resembling 
them) in egg-tubes which had not yet lost their pyriform shape ; but as a general rule, 
even in specimens as far advanced as Plate XVIII. fig. 6, few, if any, could be per- 
ceived. Soon, however, after the germinal vesicle ceases to be visible they make their 
appearance, and rapidly increase in numbers, apparently at the expense of the oil- 
globules and surrounding fluid. 
At an early period they are small, not exceeding -gifoo diameter, but in more 
mature ova they vary from -^(^o to ‘soVo- 
Weak solutions of acetic or tartaric acid dissolved the yelk-cells, or at least rendered 
them invisible, and left instead a flocculent mass. 
In the greenish eggs of Phryganea, as described by Zaddach, the colour is owing to 
the yelk-globules themselves. In Coccus this is not the case. The yelk-globules are 
slightly yellow, and the green hue of the eggs is at first owing to the green granules, 
which I have aheady mentioned as being perhaps only very minute oil-globules. 
When, however, the egg is full-grown, and the upper chamber has been absorbed, 
these green granules will be found to be replaced by dark-green globules, regular in size, 
and about -gifo o diameter, and which appear, therefore, to be in no way represented 
in the yelk of Pliryganea eggs. 
The vitelline membrane is formed so gradually that it is difficult to ascertain the exact 
time of its formation ; when,*however, the egg is full-grown, it may clearly be seen to 
be enclosed by this membrane, which is firm in texture, quite colourless, and shows no 
structure. 
I could see no trace of micropyle, which under the circumstances is quite naturaP 
The mature egg is a light green, oval mass, -afwo length and o breadth. It 
is enclosed in an outer structureless membrane, probably the vitelline membrane, but, 
like Steix*, I never could find a trace of a second, though the eggs of most insects are 
generally said to have double covering. 
Since these eggs are hatched almost immediately after leaving the body of the mother, 
it is evident that they do not require so thick a shell as those which are deposited in 
* Loc. cit p. 66. 
