the Glall-flies of the Oak. 285 
explanation. M. Adler, on the other hand, proves its falsity 
as regards the galls of the Cynipide of the oak. At the 
same time he admits that it holds good in the case of certain 
galls which owe their existence to other Hymenoptera. 
Thus, the wound made by the serrated ovipositor of Nematus 
Vallisnierti in the leaves of Salix amygdalina causes an 
abundant formation of cells; and the gall thus formed attains 
its full growth at the end of a few days, before the larva has 
escaped from the egg. In the Cectdomyie, on the contrary, 
the manner in which the eggs are laid shows clearly that it 
is the larva which causes the formation of the gall. The 
same is the case with the Cynipide. No effect is produced 
until the larva is hatched. Zrigonaspis crustalis lays its 
egos in May, and the larve do not hatch till September; and 
it 1s only in this last month that the gall begins to form. As 
soon as the larva has attacked some cells the increase is 
effected. M. Adler has even proved that whilst the young 
larva has the hind part of its body still enclosed in the mem- 
brane of the egg, a large proliferation of cells is formed 
in front of it round the slightly wounded tissue. M. Adler 
gives many particulars concerning the regions of the tree 
and the nature of the tissues in which the galls are deve- 
loped, and concerning the causes which lead to anomalies or 
arrests of development of these galls. [Two coloured plates 
very well executed represent the galls mentioned in the 
memoir.! The author. describes and figures with care the 
parts of the ovipositor, and discusses the manner in which 
the egg is probably introduced to the further end of the canal 
pierced by the insect. 
The eggs of the gall-flies differ from the pedicellated eggs 
of other Hymenoptera in so far that in the latter the pedicel is 
placed at the anterior pole of the egg instead of at the poste- 
rior. Moreover this extension is not a simple solid appen- 
dage of the envelope of the egg of cuticular nature. It 
contains a cavity which is in direct communication with the 
vitelline cavity; and its extremity presents a club-like swelling. 
M. Adler is of opinion that this pedicel, which is exposed to 
the atmosphere, performs the part of a respiratory tube. 
We have already pointed out above some of the essential 
characters which distinguish the two generations in certain 
Cynipide. ‘The distinction is far from bemg always so 
striking as that which is observed in the group Biorhiza. 
The species of Newroterus and Spathegaster do not exhibit 
externally much difference; but on examining them more 
closely it is seen that the Neuwroterus form is thicker set and 
has the abdomen more strongly developed, the wings shorter 
