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Alternating Generations

A Biological Study of
Oak Galls and Gall Flies 7 '^ /

By Hermann Adler^ M.D.
Schleswig

TRANSLATED AND EDITED HY
CHARLES R. STRATON

F.R.C.S. Ed., F.E.S.

WITH ILLUSTRATIONS

Oxford

AT THE CLARENDON PRESS

1894

VKINTEIJ AT THE CLARENDON PRESS
BY HORACE HART, PRINTER TO THK VNIVERSITY

EDITOR'S PREFACE

While pursuing the study of galls as a branch of
comparative pathology, I was fortunate enough to
become acquainted with Dr. Adler's monograph of
Alternating generations in oak gall-flies.

The originality of the matter, and the important light
which it threw on some of the great biological problems
of the day, induced me to ask his permission to publish
it in an English dress. I have to thank him for the
generous manner in which he placed his work, and the
beautiful drawings which accompanied it, at my disposal.
Unfortunately the stones from which the illustrations
were printed had been broken up, but I venture to
think that they have been very faithfully reproduced.

In the Introduction, and especially in the description
of Cynips Kollari in the Appendix, I have used freely
the writings of Dr. Beyerinck and Professor Mayr.
1 have added an analytical table of galls, a short
bibliography, and a list of the Cynipidae. I have
enclosed my own notes to the text in brackets, and
in these I have given the synonyms of each species,
its popular name, the inquilines and parasites which

vi Editor s Preface.

have been reared from it, and the species of oak on
which it is recorded as having been found.

My grateful acknowledgements are due to Dr. Adler,
Mr. E. A. Fitch, and Mr. A. Ehrmann for their
assistance in correcting the proofs, and to Professor
Mayr and Baron C. R. Osten-Sacken for information
on special points.

C. R. S.

West Lodge,
Wilton,

Salisbury.

CONTENTS

PAGE

Introduction ...... By tlic Editor ix

Description of Plates . . . . . . . . xli

Alternating Generations in Oak Gall-Flies. By Dr. Adler i

Chapter I. Early Observations and Methods of

Research i

II. Descriptions OF Cynipidae Observed. Table

of Alternating Generations ... 9

III. On Gall Formation ..... 97

IV. The Ovipositor and the Egg . . .110
V. Grouping of the Cynipidae . . . 129

VI. Alternating Generation, and Cyclical

Propagation ...... 149

Pediaspis aceris and Bathyaspis aceris . . . 159

Cynips Kollari ...... By the Editor 163

Synoptical Table of Galls .... „ 168

Classification of the Cynipidae ... „ 172

Bibliography ....... ,, 182

Index ............ 191

INTRODUCTION

A GALL is an abnormal growth of plant tissue produced
by animal agency acting from within. All the natural
orders of plants include species which are liable
to be made use of by insects in this way. Each is
visited by its own special gall-maker, which need not
necessarily belong to the Cynipidae, for gall-makers
are also found among the Coleoptera, Lepidoptera,
Diptera, Nematoda\ and in other classes. Any organ
of the plant may become the seat of this hyperplasia,
but the form which the gall ultimately assumes is
governed by the potentialities of growth in the part
attacked, and by the nature of the animal excitation
present. The rose and some Compositae produce well
known galls, but the oak is the favourite home of the
Cynipidae. In this monograph Dr. Adler has described
those oak-galls and gall-flies most commonly found in
this country, with the exception of Cynips Kollari,
the Devonshire marble-gall, which does not occur in
Germany north of the Elbe ; as it is however one of
the most familiar galls on English oaks, a description
of it has been added in the appendix. Before Dr. Adler

' H. Charlton Bastian, ' Monograph of the Angulllulidae,' Lin. Soc.
Trans, vol. xxv, 1866.

X Introduction.

had demonstrated the existence of cycHcal propagation,
many curious explanations were offered, in order to
account for the lengthened interval that elapses between
the death of one generation and the appearance of the
next. The currant-gall, for example, appears on the
male catkins of the oak in May, the fly quits the gall
in June, lives for a few days only, and nothing more is
seen until the male catkin appears again next May.
What had become of the eggs in this long interval ?
Spontaneous generation of the insect, within a gall that
had no external opening, had its advocates. Later it
was believed that a form of metempsychosis took place,
and galls were among the stepping-stones in the path of
organic evolution, by which the vegetable passed into
the animal soul. By some it was supposed that the
eggs, found in the fly in June, reached the ground,
whence they were drawn up, mingled with the sap, and
arrested next spring in the leaves or flowering
catkins, there to form the currant-galls again. Dr. Adler,
by proving the existence of cyclical propagation, has
shown that the interval between the appearance of
the currant gall-fly in one spring, and its reappearance
in the next, is occupied by another agamous generation.
But while he showed that this rule holds good for the
majority of species, he has also demonstrated that, in
some at least, no sexual generation now exists.

Pliny ' knew that a fly was often produced in a gall,
but he did not associate it with the cause of gall-growth ;
on the contrary, he thought galls grew in a night, like
fungi. Many early observers, however, considered them
as insect productions and were aware that a variety of
insects emerged from them ; but the attention which
some of these authors bestowed upon this subject was

^ Pliny, Nat. Hist. xvi. 9, lo ; xxiv. 5.

Marcellus Malpighi. xi

not always due to its biological interest. Mathiolus, one
of the best of the commentators of Dioscorides, and
a believer in spontaneous generation, declared that
weighty prognostications as to the events of the year
could generally be deduced by observing whether galls
contained spiders, worms, or flies. Most of the older
writers describe gall-flies, which are now known to be
agamous, as possessing males ; but their descriptions are
often perfectly clear, and the flies can be recognized as
the males of one of the Torymidae, or of some other
species of parasite. There is no reason to think that
any males of agamous species were actually in existence
at the time when these authors wrote.

The earliest systematic writer on galls was Marcellus
Malpighi, Physician to Innocent XII. He was
Professor of Medicine at Bologna, and afterwards at
Messina, and his treatise ^ ' De gallis,' published in 1686,
gives an extremely accurate description of the galls then
found in Italy and Sicily. Dr. Derham, Canon of
Windsor, in the notes to his Boyle Lectures •(1711-1712)
compares Malpighi's account with the galls then found
in England, and says, ' I find Italy and Sicily more
luxuriant in such productions than England, at least
than the parts about Upminster (where I live) are.
For many, if not most, of the galls about us are taken
notice of by him, and several others besides that I have
never met with, although I have for many years as
critically observed all the excrescences and other
morbid tumours of vegetables as is almost possible,
and do believe that few of them have escaped me ^.'

Malpighi's work does not appear to have been
known either to Linnaeus or Fabricius ; they include

' Dioscorides, i. 146, Paris, 1549.

* W. Derham, F.R.S,, Physico-theology , iii. c. 6.

xii Introduction.

inquilines and parasites under the genus Cynips, indeed
St. Hilaire, Latreille, and Olivier reserve the name
Cynips for certain Chalcididae, and use Diplolepis for
the true gall-maker, but with few exceptions subsequent
writers have applied the general name Cynips to the
gall-makers. It is well, however, to bear this change of
nomenclature in mind, when the males of certain species
are said to have been found \ Reaumur has left
excellent descriptions and drawings of many species of
galls '", but the first to bring order out of the confusion
in which the Cynipidac still remained, was Theodor
von Harlig of Brunswick^. He greatly improved the
existing classification of this family and carefully pointed
out the true relationship which the various dwellers in
galls bore to each other. He arranged gall inhabitants
into three classes ; first, the gall-makers which he com-
pared to the actual householders ; secondly, inquilines,
guest-flies, cuckoo-flies or lodgers, who take up their
quarters uninvited within the gall, and live on its food
stores, but do not directly aim at the gall-maker's life ;
and thirdly, parasites who deposit their eggs on the
larvae of their host or his lodgers, with the object of
destroying them, and who are therefore murderers.
Besides those living in a state of symbiosis, there are
also true commensals in some galls.

It is the simultaneous presence of these various classes
that frequently gives rise to confusion in carrying out
breeding experiments. Synergi among inquilines re-
semble true gall-making species so closely, that caution

' Westwood, Zoological Journal, No. 13 ; Cameron, P., British
Phyt. Hymen, vol. iii. p. 140.

'' Reaumur, Me'nioires pour servir d Vhistoire des insectes,
1734-42.

■ Hartig, ' Ueber die Familien der Gallwespen,' Gerniar^s Zeitschr.
f. d. Ent. II. Heft i. p. 176, 1840; III. 322-358, 1841 ; IV. 395, 1843.

Gall- Dwellers. xiii

is always necessary to see that the gall-maker, and not
a Synergus, has been obtained \ Both Malpighi and
Canon Derham were aware of the attacks of parasites,
and actually saw galls pierced by them. The latter says,
' I apprehend we see many vermicules, towards the
outside of many oak-apples, which I guess were not
what the primitive insects laid up in the gem from which
the oak-apple had its rise, but from some supervenient
additional insects, laid in after the apple was grown, and
whilst it was tender and soft'.' Ratzeburg, a forester
like Hartig, in his beautiful * Forstinsekten ' " corro-
borated Hartig's division of gall-dwellers. Giraud,
Schenck, Reinhard, Taschenberg, Schlechtendal,
Wachtl, Forster, and Lichtenstein, have since each
advanced our knowledge of the Cynipidae, and the
history of galls generally has been admirably written by
Lacaze-Duthiers. The entomologists of America have
not been behind those of Europe ; Baron C. R. Osten-
Sacken, before he quitted America in 1877, had discovered
eighteen new species ; Bassett, thirty species, and Walsh
and Riley had each added much to our knowledge.
Professor Gustav Mayr of Vienna has not only increased
largely the work of previous observers, but has
arranged all that is known of gall-makers and gall-
dwellers in a series of admirable monographs * and has

' See Walker, But. Mag. vii. p. 54.

' Derham, Physico-theology, iii. p. 389.

' Ratzeburg, Die Forstinsekten, vol. iii, Berlin, 1844.

* Mayr, G., Die initteleuropdischen Eichengallen in Wort und Bilderu,
Wien, 1870-71 ; Die Einmiethler der niitteleuropdischen Eichengallen,
Wien, 1872; Die europdischen Cynipiden-Gallen tnit Ausschluss der auf
Eichen vorkoynmenden Arten, Wien, 1876 ; Die europdischen Toryniiden .
Wien, 1874; Encyrtiden, 1876; Olinx, 1877; Eurytonta, 1878:
Telenotniis, 1879; Die Genera der gallenhewohnenden Cynipiden,'W\^n,
1881 ; Die europdischen Arten der gallenhewohnenden Cynipiden, Wien,
1882.

xiy Introduction.

drawn up excellent analytical tables of species. In this
country Westwood, Halliday, Walker, and Fitch have
all done good work, and Mr. Peter Cameron^, in
his account of the Phytophagous Hymenoptera, just
completed for the Ray Society, has brought together
an immense amount of valuable material, new and
old.

Dr. Adler began his observations on gall-flies in 1875,
and added certain new species described in these pages.
His important work, however, was the unfolding of
their life-history ; proving that while many species were
linked together in alternate agamous and sexual genera-
tions, others remained wholly agamous.

Among biologists theories of dimorphism and meta-
genesis had been discussed in connexion with the
Cynipidae and were current as early as 1865 '^ ; in 1873
Bassett announced his theory of seasonal dimorphism^ ;
and in the same year Riley established the existence
of alternation of generations between Cynips operator
and Cynips opcratola\ The numerous publications of
Thomas and Frank have cleared up many special
points, and Beyerinck ^ in an admirably illustrated
monograph, full of original work and careful reasoning,
has added much both from a botanical and zoological
point of view.

The existence of alternating generations in living

' Peter Cameron, A Monograph of the British Phytophagous
Hymenoptera, 4 vols. 1882- 1893. Ray Society.

'' Reinhard, ' Die Hypothesen iiber die Fortpflanzungsweise bie den
eingeschlechtigen Gallwespen,' Berlin. Ent. Zeitschr. vol. ix. 1865.

■' Bassett, Canadian Entomol. vol. v, pp. 91-94, May, 1873.

* Riley, American Naturalist, vol. vii. p. 519, 1873.

' Beyerinck, Dr. M. W., ' Beobachtungen iiber die ersten Entwick-
lungsphasen einiger Cynipidengallen,' Natnurk. Verh. der Koninkl.
Akademie, Deel xxii.

Cyclical Propagation. xv

organisms was first discovered by Chamisso', the author
of Peter Schlemihl,' who in 1815 accompanied the Chan-
cellor Rumjanzow's expedition as naturalist in a voyage
round the world. He noticed that among the Salpae
a solitary salpa gave rise to a generation of a different
form, united in chains of twenty or more, and that each
link of this ' associated ' form again produced the
' solitary ' form. He concluded that all solitary salpae
produced chains, and on the other hand that all those in
associated chains were the parents of solitary ones ; so
that a salpa mother was not like its daughter or its own
mother, but resembled its granddaughter and its grand-
mother. At first the accuracy of Chamisso's observations
was doubted, chiefly for the reason that no similar
phenomenon was then known in nature. By degrees,
however, facts began to accumulate ; in hydroids and
flukes similar generation-cycles were observed, and in
1842 Steenstrup^ collected all that was known on the
subject of alternating generations into a monograph
published in Danish and subsequently translated into
German and English. He described this mode of
reproduction as ' a peculiar form of fostering the young
in the lower classes of animals.'

In 1849 the late Professor Owen^ suggested the
existence of a residual germ-force in the cells of the
apparently asexual generation, and thought that alter-
nating generations were due * to the retention of certain
of the progeny of the primary impregnated germ-cell, or
in other words to the germ-mass, with so much of the
spermatic force inherited by the retained germ-cells from

' Adalbert de Chamisso, De Animalibus, Fasc. i, De Salpa, Berlin,
1819.

^ J. J. S. Steenstrup, Ueber den Generationswechsel, Kopenhagen,
1842, and Ray Society, T845.

^ R. Owen, Parthenogenesis, 1849.

xvi Introduction.

the parent cell or germ-vesicle, as suffices to set on foot
and maintain the same series of formative actions as
those which constituted the individual containing them ' :
and this may be taken as the earliest suggestion of the
continuity of the germ-plasm.

Fresh instances of this class of phenomena have
steadily accumulated, in which the life-cycle of the
species may be represented by two or more generations,
differing in form and organization, existing under
different conditions, and reproducing themselves in
different wa3's.

The simplest cyclical rhythm occurs in reproduction
by metagenesis, where a sexual and asexual form
alternate ; this is the law of development in Medusae
and Trematoda. In heterogenesis a sexual and an
agamous generation alternate, and in this rhythm the
agamous may be juvenile or adult ; in Cecidomyia, for
example, the parthenogenetic generation reproduces
itself when still immature, while in the Cynipidae, on the
other hand, it does so only when perfectly developed.
Another variety occurring between one hermaphrodite
and one sexual form, is seen in Angiostomiirn nigro-
venosum, the lung parasite of the frog ; and a still more
perfect alternation is found in the thread worm of the
snail, Leptoptera appcndiculata, where two perfectly
formed sexual generations are linked in a cycle.

Sometimes the sexual or asexual member of the cycle
may be complex. The liver-fluke of the sheep gives
rise to an active ciliated aquatic embryo, which, after
a time, pierces and enters a water-snail to become
a passive sporocyst; from its germ-cells fcdiaesLve formed
within the sporocyst, and after several asexual genera-
tions, they give rise to minute ccrcariae, which leave the
snail and creep up the stalks of grass ; here they

The Larval Theory. xvii

become encysted, are eaten, and grow within the sheep to
become adult sexual flukes. In this series the Cercaria
and fluke form members of the sexual division; all the
others are members of the asexual division of the cycle.

In all C3'clical propagation, whether in the animal or
vegetable kingdom, there is a tendency for one genera-
tion to become subordinated to the other. In flowering
plants the sexual is subordinated to the asexual, and
even some ferns exhibit a similar tendency, a fern-
plant rising vegetatively from the prothallus ; while in
other ferns there is a tendency to apospory, a fern-
prothallus springs from the site of the spores, and the
asexual becomes subordinated to the sexual. In flukes,
in the same way, rcdiac ma}^ be budded off frofn the
sporocyst and the species be continued without ever
attually becoming sexual. In the Cynipidae it will be
seen that in some, like Cynips Kollari, the sexual genera-
tion has been wholly subordinated to the asexual, and
in others, like Rhodites rosae, this process is still going
on and males are becoming functionless and extinct.

Leuckart^ regarded interpolated generations as larval
states, and following his teaching, Lichtenstein ^ looked
upon the agamous as larval stages of the sexual species.
He believed that the biological evolution of a gall-fly
extended from the time when a female emerged from
a true egg in a condition to be fecundated by the male,
until another egg was reached presenting the same con-
ditions. All other stages he considered as larval, al-
though in them reproduction by budding was possible,
and he held that in this way insects might go on re-
producing themselves indefinitely without ever reaching

' R. l^QucksLtX, Znr Keniitiiiss d. Generationswcchscls ltd. Parthenog.
b. d. Insektcn, 1858.

- J. Lichtenstein, Les Cyutpides, 188 1, p. x.

b

xviii Introduction.

the perfect state. Certain Phylloxeridae reproduce
themselves by subterranean budding, without ever arriv-
ing at the winged and sexual forms : he regarded this
as analogous to the multiplication of plants by suckers,
without the intervention of seed. He compared the
life-history of gall-flies with that of Phylloxera, and gave
it as his opinion that, among the gall-flies, the individuals
o^ Neuroterus lenticular is had been mistaken for females,
because they possessed an ovipositor and eggs, that,
properly speaking, they had no sex, but were only larval
forms of Spathegaster baccarum, their so-called eggs
being gemmations.

It is difficult to regard species which have a perfect
female form, and ovaries filled with perfect eggs, as
being perpetually in the larval state, because they are
wholly agamous and have no males. In Rhodites rosae,
as has been said, the few males found are functionless,
and are disappearing; it seems therefore more in
accordance with facts to speak of the individuals of
agamous species as females, the males of which have
ceased to appear. Although the Aphides are scarcely
comparable to the Cynipidae, since they possess a form
which is asexual, they may nevertheless be arranged,
like the Cynipidae, in alternate generations, without
having recourse to the larval theory.

The importance of sexual reproduction has been
greatly exaggerated, and there seems no good ground
for assuming that a generation ought to extend from
one fecundated egg to another. In Cynips Kollari, and
many others, no sexual generation is known ; the flies
all possess perfect female forms, but they are agamous
and have the power of reproducing themselves by
parthenogenetic eggs. At the same time it is difficult
to believe that the agamous can be the primitive

Advantages of Parthenogenesis. xix

form ; or that perfectly formed sexual organs could
have been evolved unless the sexual had been the
earlier generation.

The power of producing parthenogenetic eggs is
widely distributed among the arthropods, and appears
to come into operation whenever it secures the existence
of the species more effectually than sexual reproduction.
When at one season of the year sexual, and at another
agamous, reproduction is the more beneficial, then
heterogeny will be found to prevail. In one group
amphimixis has been wholly abandoned, but its members
are enormously prolific, and their eggs have the power
of resting over more than one year. By means of
partial parthenogenesis, a much more rapid increase
is ensured than could have been possible, in the same
time, by sexual reproduction only. Every individual
of the winter generation, unhindered by the require-
ments of fertilization, is engaged in laying eggs ; the
number of the sexual individuals hatched from these
eggs is consequently enormously greater than it could
have been, had only half the winter generation been
of the female sex, and had that half, in order to be
fruitful, been dependent on the chances of fecundation.
When generations alternate, there are alternating
advantages to the species. The winter generations
emerge from the gall at a time when pairing is not
easy, and it is a distinct gain to the race when every
individual has the power of reproducing itself inde-
pendently. The summer generations, on the contrary,
appear in halcyon days, when there is nothing to mar
their nuptial flight, and then the species obtains greater
variation, and those physiological advantages of amphi-
mixis which parthenogenesis cannot afford.

But amphimixis is in no way essential to heredity.
b2

XX Introduction.

The oak gall-flies about to be described will be found
to afford examples of heredity occurring among purely
agamous species, as well as among those which alternate
between an agamous and a sexual generation. The
characters of each generation are inherited and passed
on in two perfectly distinct streams. The advance
which has in recent times been made towards a clearer
comprehension of heredity, is in great measure due
to the influence of Weismann ', who, by discarding the
idea that sexual reproduction is in any way funda-
mental or essential to life, has led us to regard the
facts of heredity wholly untrammelled by it. Amphi-
mixis undoubtedly has its advantages, but descent may
be continuous in the female line, or there may even
be a male parthenogenesis ^

To understand the mechanism by which alternation
of generations is brought about, it is necessary to recall
the minute structure of the sexual cells, and especially
the behaviour of their nuclear contents ; and to observe
the difference in the extrusion of the polar cells, as
occurring in the eggs of parthenogenetic and sexual
species.

The changes in the ovum during nuclear division
are briefly these '. After a resting stage the chromatin
granules, which there is reason to believe are the
material bearers of hereditary qualities, appear as
a thread, apparently, spirally coiled within the nucleus.
An accessory nucleus forms and divides into two ;
at each pole of its achromatic spindle is placed
a centrosome with its surrounding attraction-sphere ;
the nuclear membrane disappears ; the chromatin

' Weismann, Essays on Heredity, vol. ii. p. 86, 1893.

- Ibid. vol. i. p. 253 ; Schenck, Handbitch dcr Botaitik, Bd. ii. p. 219.

^ Weismann, Essays on Heredity, vol. ii. p. 118.

spermatogenesis. xxi

granules become aggregated into rod-like chromosomes
of equal length and of constant number in each species ;
these are formed at the equator of the spindle, and
split by longitudinal fission, so that their number
becomes doubled. One star of chromosomes is drawn
to the centrosome at each pole of the spindle, and thus
two daughter-nuclei, which for convenience I will term
oocytes, are formed, of unequal size ; the smaller one
being extruded as the first polar body. In the
parthenogenetic egg this completes the division, but
in the sexual egg a second nuclear division follows
immediately on the first without a resting stage ; the
oocyte divides into two oozoa, and one oozoon, contain-
ing half the chromosomes, is extruded as the second
polar body. The oocyte which forms the first polar
body is observed to split into two oozoa after extrusion.

In this way three of the oozoa which have arisen
from the division of the primitive germ-cell have
become polar bodies, while the remaining oozoon,
containing one half the number of chromosomes which
the primitive germ-cell contained, is left in the nucleus,
functional or capable of development.

Within the spermatic tubes of the male, corresponding
changes take place in the primitive sperm-cell. Its
chromosomes are doubled and it divides into two sper-
matocytes (spermatogens), each of which again divides
without a resting stage into two spermatides (spermato-
blasts). The four spermatides undergo various changes
during which they become elongated, the nucleus,
containing the chromatin elements, becomes the head
of a spermatozoon and ends in a motile barb. The
protoplasm of the cell-body is drawn out into a sheath
through which the filament passes, and is continued
beyond as the vibratile tail.

xxii Introduction.

We have therefore this arrangement of parts in the
male and female cells, to which for convenience of
comparison I will apply these names.

I. Primitive germ-cell. = Primitive sperm-cell.
II. Two oocytes of = Two spermatocytes,
which one forms
the first polar
body.
III. The oocytes dividing = The spermatocytes di-
into four oozoa, of viding into four sper-

which two are pri- matides, each becoming

marily functional a spermatozoon, two of

in the partheno- which may become re-

genetic and one in productive in a male

the sexual egg. parthenogenesis, one is

primarily functional in
the sexual egg.
There seems little doubt that the chromosomes
containing the germ-plasm of the species, are identical
in the maternal and paternal reproductive cells, and that
so long as their number is complete or sufficient to enable
conjugation to take place, it is immaterial from which
parent they may come. Boveri ' succeeded in denucleat-
ing the egg o^ Echinus microtuberculatus and introducing
spermatozoa of another species, Sphaerechinus granu-
laris ; when the egg developed, the larva was found
to belong to the latter species, although living on the
vitellus of the former. This was a case of male
parthenogenesis. It however appears certain that one
oozoon or spermatozoon requires conjugation with
one other oozoon or spermatozoon before development
can take place.

* Boveri, ' Ein geschlechtlich erzeugter Organismus ohne miitter-
liche Eigenschaften, ' Gesells./. Morph. u. Phys. Munchen,Ju]y i6, 1883.

The Germ-Plastn. xxiii

According to Weismann, the chromosomes are
'idants,' formed of smaller groups called 'ids'; these
are made up of ' determinants,' which are again
composed of ' biophors ' or ultimate units. The biophors
are more or less equivalent to the ' physiological units '
of Herbert Spencer, the 'plastidules* of Haeckel, the
' gemmules ' of Darwin, and the ' pangenes ' of De Vries ;
although these variants are not exactly analogous to
each other, they are all ultimate molecules of inherited
plasm ^. The nuclear thread is, so to speak, the web of
the individual's destiny, and the ids which it contains
are the inherited working plans of its architecture. As
development advances, the ids are disintegrated into
determinants, and the determinants into biophors, each
group getting smaller until every biophor ultimately
reaches and controls its own cell. The way in which
the germ-plasm assumes the direction of ontogeny
resembles a battalion marching to outpost duty. The
main body steadily proceeds to distribute itself accord-
ing to a predetermined plan ; the battalion splits into
half-battalions, the half-battalions into companies, the
companies into pickets, and the pickets tell off their
sentries, until each man at last finds himself at the
post he has to guard. And just as a line of communica-
tion is always maintained through the battalion, so each
nucleus is kept in touch with its cell, and each cell
with the cells around it, by means of a fine protoplasmic
reticulum which passes through the cell-walls'-. It is
obvious that influences affecting any stage of develop-
ment must affect larger or smaller groups of deter-
minants, just as any command given by an officer will

^ Weismann, Germ-plasm, p. 41.

^ Sedgwick, Monograph of the development of Peripatiis capensis,
p. 41.

xxiv Introduction.

affect the number of men particularly under him, and
may alter their original course.

In cases of alternation of generations, and in those
cases in which the two generations do not differ from
each other in the full-grown condition, but in which
the eggs develop differently, Weismann holds that
there must be two kinds of germ-plasm, each containing
the determinants of one form, and that these two must
be passed separately along the germ-tracks, from one
generation to another, so that each must always contain
the other, stored away in an inactive condition \

In the case of gall-flies there is often a well-marked
difference of structure between the females of the two
alternating generations. The wing determinants in the
winged Trigonaspis crustalis (Plate II, fig. i8 a) must
have been modified in the wingless Biorhiza renum,
(Plate II, fig. i8), but they appear again in Trigonaspis
crustalis. It is improbable that lost determinants
would be redeveloped in this way, and therefore there
must be two alternating sets of determinants. These,
Weismann holds, are contained within the same germ-
plasm, but never become active at the same time ^

I believe that in the function of the polar bodies we
possess the simplest explanation of the problem of
alternating determinants in the Cynipidae.

According to Weismann's earlier views ^, the first
polar body removed ovogenetic nuclear substance which,
after the maturation of the egg, had become superfluous
and injurious ; while the second polar body removed as
many different kinds of idioplasm as were afterwards
introduced by the sperm-nucleus.

He has abandoned this view of the function of the

' Weismann, Germ-plasm, p. 176. ^ Ibid. p. 178.

^ Essays on Heredity, vol. i. p. 365, Oxford, 1891.

Function of Polar Bodies. xxv

first polar body, and, according to his later views, the
extrusion of both polar bodies is a provision for with-
drawing promiscuously certain ids of germ-plasm for
the purpose of securing variation. He says : 'I consider
this remarkable and apparently useless process of the
doubling and two subsequent halvings of the idants, as
a method of still further increasing the number of possible
combinations of idants in the germ-cell of one and the same
individual ' ' ; the three quarters of the mass of germ-
plasm which passes into the polar bodies, he regards as
being 'again lost",' while what is left in the ovum, after
being increased by one spermatozoon, is halved by the
first nuclear division ; one half going to direct ontogeny,
and the other half going to form the primary sexual
cells : but as these last divide and behave at first like
other somatic cells, they must, he thinks, possess active
idioplasm as well as unalterable germ-plasm, and they
must therefore contain more ids in their nuclear matter
than do somatic cells ^

I incline to the view that these cells in the Cynipidae
remain somatic, and simply form the rudiments of the
sexual organs, but that the function of the polar bodies
is to provide the primitive reproductive cells. These
bodies contain the inactive germ-plasm, historically
prepared for this very purpose, and it is scarcely possible
to imagine that nature would create this phyloge-
netic epitome of the species to be extruded as func-
tionless, or to be broken up and again lost *. It is
undeniable that they are of great value in promoting
variation. The first division of the nucleus into two
oocytes is not a reducing division, but results, so far as
the germ-plasm is concerned, in two equivalent cells.

' Weismann, Gerni-plastn, p. 247. - Ibid. p. 248.

^ Ibid. p. 192. * Ibid. p. 248-

xxvi Introduction.

In the sexual egg, however, the second division follows
immediately upon the first, and the extrusion of one
oozoon reduces the chromosomes by half their number,
which is again made good by those of one spermatozoon.
While, therefore, in the parthenogenetic egg those
'material bearers of ancestral qualities' remain the
same from generation to generation, they are changed
in the sexual generation by each cross fertilization, and
in this exists the advantage of amphimixis. For the
evolution of species, individual variation is essential,
and those individuals who derive half their germ-plasm
from one parent, and half from another, each bringing
in different lines of ancestors, must present greater
variation than those who derive their germ-plasm from
one parent and one ancestral line. Sexual reproduction
is thus of advantage to the species in so far as it helps
to increase inherent tendency to variation, and enables
evolution to take place by the steady accumulation of
slight beneficial differences '. The random withdrawal of
the ids of ancestors by a species of lot, as laid down by
Weismann, must be considered simply as a provisional
hypothesis ; and it seems, according to Prof Hartog,
that mathematically its effect, if it took place at all,
would be the opposite of what Weismann expected "^

Although the polar bodies were first noticed by
Miiller in 1848, their importance has only been recently
appreciated. Balfour^ considered their extrusion as
the removal of part of the constituents of the ger-
minal vesicle which are necessary for its functions as
a complete and independent nucleus to make room for
equivalent parts of the spermatic nucleus ; and he con-

' Darwin, Origin of Species, p. 132.

2 Prof. Hartog, Nature, vols, xliv and xlv, 1893.

^ F. M. Balfour, Comparative Embryology, vol. i. p. 63, 1880.

Embryonic Germ- Cells. xxvii

sidered that the function of forming polar cells had
been acquired by the ovum for the express purpose of
preventing parthenogenesis. Van Beneden * and Minot'''
regard the polar bodies as male elements removed from
a hermaphrodite cell. Butschli, Hertwig ^, and Boveri
incline to regard them as abortive ova and an atavistic
reminiscence of primitive parthenogenesis. Geddes and
Thomson * consider their extrusion due to the tendency
of every cell to divide at the limit of growth, but favour
the view that the process may be an extrusion of male
elements. They consider, however, that these cells have
no history, though they occasionally linger on the
outskirts of the ovum, are seen to divide, and be
penetrated by ' misguided ' spermatozoa ^

The homologous character of oozoa and spermatozoa
has been pointed out, and these so far retain the habits
of their protozoan ancestors as to require conjugation:
in the parthenogenetic form, the two oozoa conjugate
in each oocyte, in the sexual form one oozoon and
one spermatozoon unite to form the fertilized ovum
or oosperm, but I believe the three oozoa which
form the polar bodies, unite together or conjugate
with three spermatozoa, previous to that repeated
division by which those bodies are prepared to be
received as the earliest embryonic germ or sperm-cells
into the rudimentary germ-tracks''.

^ E. Van Beneden, ' Recherches sur la fecundation,' Arch, de
Biologie, iv, 1883.

^ C. S. Minot, 'Theorie der Genoblasten,' Biol. Coitialbl. ii. p. 365.
^ O. Hertwig, Die Zelle und die Gewebe, Jena, 1892.

* Geddes and Thomson, Evolution of Sex, p. 107, 1892.

* Ibid. p. 105.

® H. Henking, Zeitschr. f. wissensch. Zoologie. liv. 89 ; V. Graber,
' Keimstreif der Insecten,' Denkschrift d. K. K. Akad., Math.-Nat. CI,
Wien, Ivii, 1890.

xxviii Introduction.

The division of the primitive sperm-cell into four
takes place in the seminal tubes, each fourth becoming
subsequently a spermatozoon ; while the corresponding
division of the primitive germ-cell is that associated with
the extrusion of the polar bodies. As soon as one
spermatozoon enters the ovum, Fol describes the
vitelline membrane as appearing to rise up, to prevent
the entry of other spermatozoa into it. The polar
bodies lie above this membrane, and between it and
a thinner layer, so that even if this were the case,
other spermatozoa are not hindered from reaching
them. Spermatozoa in numbers are constantly
seen entering the ovum, and especially the polar
eminences.

In order to trace the disposal of the germ-plasm
present in the nucleus, the egg of Ascaris niegalo-
cephala {hivalens) may be taken as the most thoroughly
worked out. In it the primitive sperm-cell contains
four chromosomes, which become doubled in the first
spindle, after which the cell divides into two sperma-
tocytes, each containing four chromosomes and their
respective centrosomes. Each spermatocyte divides
into two spermatides, and each of the four sperma-
tides becomes a spermatozoon with two chromosomes.
In the primitive germ-cell the four chromosomes
become doubled in the first spindle, the nucleus divides
into two (oocytes we may term them for convenience),
one oocyte remains in the ovum with four chromo-
somes, and the other oocyte with its four chromosomes
becomes the first polar body, which breaks up into two
oozoa with two chromosomes in each. The oocyte
remaining in the nucleus, without any resting stage,
undergoes a second division into two oozoa : one
oozoon containing two chromosomes is extruded as the

RedB

Fig. I.

Diagram of the formation of spermatozoa in Ascaris 7)iegalo(ephala,
var. bivaletis. (Modified from O. Hertwig.) A. Primitive sperm-cells.
B. Sperm-mother-cells. C. First nuclear division. D. The two
daughter-cells, or spermatocytes. E. Second ' reducing ' division.
F. The four grand-daughter cells, the sperm-cells, or spermatides, each
becoming a spermatozoon.

To/ace p. xxviii.

Red.i

Fig. II.

Diagram of the formation of ova in Ascaris megalocephala, var.
bivalens. A. The primitive germ-cell. B. Fully (leveloped germ-
mother-cell, with chromosomes doubled. C. The first nuclear division.
Jh One daughter-cell (oocyte) extruded as the first polar body. E. The
second or reducing division ; the retained, and the extruded oocyte,
dividing, and forming four grand-daughter cells (oozoa). F. The ripe
egg-cell, the functional oozoon ; the oilier oozoa, 2, 3, and 4, being
the polar bodies.

Conjugation of Polar Bodies. xxix

second polar body, and one oozoon is left containing
the remaining two chromosomes.

Assuming that the egg of one of the parthenogenetic
species of Cynipidae had the same number of chro-
mosomes as the species of Ascaris just described, four
chromosomes would be extruded as the first polar body
and four would remain in the nucleus. In that of a
sexual species, on the contrary, six chromosomes would
be found in the polar bodies and only two in the nucleus ;
but when fertilization took place, two chromosomes
would enter the ovum with one spermatozoon, and six
chromosomes would be added to the polar bodies when
three other spermatozoa united with them. Thus the
polar bodies of one egg of the parthenogenetic generation
would contain four chromosomes available for the supply
of germ-plasm to the next generation ; while the polar
bodies of a sexual egg would afford twelve chromosomes
for the germ-plasm of the generation that follows. It is
clear that if the polar bodies contain the germ-plasm of
the next generation they must be fertilized by three
spermatozoa, since in the sexual generation male and
female characters are equally transmitted. If this be
the case, we ought to find the eggs of the parthenogenetic
generation much more numerous than those of the
sexual, because the parthenogenetic germ-tracks have
received the produce of twelve, while the germ-tracks
of the sexual generation have only received that of four
chromosomes ; and it is to be presumed that the ova
produced from them would bear something like this
proportion to each other, if this theory held good. What
are the facts ? The summer sexual generations, whose
germ-plasm has been received from the parthenogenetic
polar body, produce from 200 to 400 eggs ; while the
winter agamous generation, which receives its germ-

XXX Introduction.

plasm from the fertilized polar bodies of the sexual
generation, produces from i,ooo to 1,200 eggs; or in an
approximate proportion to the number of chromosomes
postulated as present.

The impression which long prevailed that one sperma-
tozoon was equal potentially to one ovum, led observers
to regard the presence of more than one spermato-
zoon as an act of ' polyspermy,' as abhorrent to nature,
and a cause of monstrosity \ But Kupffer, Benecke
and others record the fact that spermatozoa do enter the
' peculiar protoplasmic protuberances/ many appearing to
form pronuclei after gaining access to the ovum, so that
in numerous species polyspermy appears to be the rule.

A great deal has recently been done in working out
the development of the reproductive rudiment in insects,
and it seems that the cells which become the ova, and
which I believe to be chiefly those primarily set
aside in the polar bodies with or without corresponding
spermatozoa, can be traced to the rudiment of the germ
and sperm-tracks of the embryo. These germinal track-
cells, formed by the first segmentation, surround the
primitive germ-cells to form with them the rudimentary
reproductive organs. In the germogen one germ-cell
and a nutritive circle of germinal epithelium cells form
a cluster, and these grow forward together, the ger-
minal epithelium growing in between each batch. In
the upper part of the developing egg-tube, each batch
is very small, but as it advances it increases steadily
in size. In the egg-tube of the Cynipidae the egg-stalk
curves round the next egg, and the clubbed end of the
stalk gives the appearance of a large and small eg'g
alternating.

In some asexual species of Hemiptera the oocyte,

^ Selenka, Y.., Befntchtung des Etes, 1871.

Alternating Streams. xxxi

which would become in an agamous species the first
polar body, is not actually extruded but may be seen as
a smaller cell lying close to the nucleus ; and in some
sexual eggs, both polar bodies are similarly retained.

It will be apparent how simply this view of the
functions of the polar bodies in Cynipidae accords with
the facts of alternating generations.

The fly which emerges from the gall of SpatJicgaster
baccarum in June is sexual, and lays an ^^^ which
extrudes two polar bodies. The germ-plasni in these
polar bodies after being united with that of three sperma-
tozoa, is received by the embryo germ-tracks of this
egg, and when from that egg the agamous Nciirotcrus
lenticularis emerges in April, it is this germ-plasm
which forms the nuclei of the ova contained in its
tubes, consequently these ova can only reproduce the
sexual flies of SpatJicgaster baccarum.

Again, the agamous Neuroterus lenticularis lays an
egg which extrudes one polar body. The germ-plasm
in this polar body is received by the germ-tracks of the
embryo, and, when from that egg the sexual Spathegaster
baccarum fly emerges, it is this germ-plasm which forms
the nuclear matter of the ova and spermatozoa contained
in its tubes, and consequently these ova and spermatozoa
can only reproduce the agamous fly of Neuroterus
lenticularis.

The two streams of germ-plasm are thus going on
independently, and are each capable of acquiring and'
accumulating beneficial variations, so that the general
dictum of Weismann is correct : 'the basis of the alterna-
tion of generations as regards the idioplasm, must, in all
cases, consist of a germ-plasm composed of ids of at
least two different kinds, which ultimately take over
the control of the organism to which they give rise.' In

xxxii Introduction.

this way we have a means not only of securing variation,
but of maintaining the fixity of species, which is equally
important.

Alternating generations disappear as we ascend higher
in the animal and vegetable scale, or as life lengthens
beyond the period when seasonal alternation could be
of advantage; then the purpose in view seems to be the
approximation and assimilation of consecutive genera-
tions, and the continuous uniformity of the species.
It is not quite clear how this result is attained, but the
polar bodies cease to monopolize the transmission of
the unalterable germ-plasm; probably another nuclear
division, after fertilization and before ontogeny has
begun, is added to them \ and well marked atavism
is only found as a pathological occurrence when the
assimilating forces fail.

It is next of interest to inquire how the various
structures of the gall came to be evolved. It may be
taken as perfectly certain that the tree does not form
them in a disinterested manner for the sake of the
Cynips, Darwin says : ' If it could be proved that any
part of the structure of an}' one species had been formed
for the exclusive good of another species, it would
annihilate my theory, for such could not have been
produced through natural selection -.' So far as galls
ace concerned, Darwin's theory is perfectly safe. The
'excitatory emanations,' as Professor Romanes^ aptly
calls them, which lead to gall-growth, can only have
arisen by gradual and increasing improvements in the
initial stages of their formation, acting through natural
selection, over an unlimited period of time, and through
numerous consecutive species

' Weismann, Germ-plasm, p. 192. - Darwin, Origin of Species,

chap. vi. ^ Romanes, Nature, vol. xli. p. 80, 1889.

Classification of Galls. xxxiii

Galls may be arranged in groups of gradually
increasing complexity, beginning with those like Spathc-
gaster baccarum, and leading up to the complicated
structure of Cynips Kollari. Beyerinck's classification
following that of Lacaze-Duthiers, is into five groups : —

1. Simple galls, consisting of nutritive tissue enclosed

in thin-walled parench3^ma with vascular bundles :
Neuroterus ostreus, Spathegastcr albipes, S.
baccarum, S. Aprilinus.

2. Galls similar to these, but having the nutritive tissue

first enclosed in sclerenchyma, which forms an

' inner gall ' :

Neuroterus lenticularis, N. laeviusculus, N.
numismatis, N . fumipennis, Aphilotrix Sieboldi,
A. autumnalis, A. radicis, A. globuli, Andricus
curvator, Biorhiza renum, B. aptera.

3. Galls possessing an inner gall like the last, but

having it surrounded by thick-walled parenchyma :
Dryophatita longiventris, D. divisa.

4. Galls with the inner gall enclosed in a spongy layer

of branched parenchyma, with wide intercellular
spaces, and having the surface covered with
a differentiated epidermis :

Unilocular. Dryophanta scutellaris.

Multilocular. Teras tcrminalis.

5. Galls which have the inner gall enclosed in thick-

walled parenchyma, and then in spong}' tissue ;
and which have a diiTerentiated epidermis :
Cynips Kollari.
Besides these histological differences, the outward
characters are also of varying complexity ; each infini-
tesimal improvement, which has been of service as
a protection against parasites, or has been successful in
securing natural conditions favourable to the life and

xxxiv Introduction.

growth of the larva, has been preserved, and has
formed the starting-point of further beneficial variations.
It is always that larva which has been able to induce
successful morphological abnormalities, which is re-
produced to continue the race ; the unsuccessful
perish. The ruling force is natural selection ; it is
impossible that intelligence or memory can be of any
use in guiding the Cynipidae ; no Cynips ever sees
its young, and none ever pricks buds a second
season, or lives to know the results that follow
the act. Natural selection alone has preserved an
impulse which is released by seasonally recurring
feelings, sights, or smells \ and by the simultaneous
ripening of the eggs within the fly. These set the
whole physiological apparatus in motion, and secure
the insertion of eggs at the right time, and in the
right place. The number of eggs placed is instinctively
proportionate to the space suitable for oviposition, to
the size of the fully grown galls, and to the food sup-
plies available for their nutrition. Dryophanta sciitcllaris
will only place from one to six eggs on a leaf which
Neuroterus lenticularis would probably prick a hundred
times. The veins and petiole of the leaf carry onwards
water and salts derived from the soil, and return the
organic products of the leaf-cells ; and these food
currents render them desirable situations for gall-
growth. The under surface of the leaf is folded out-
wards in the bud (vernation conduplicate), so that
it is the first part reached, when buds are pricked.
When expanded leaves are pricked, the spongy meso-
phyll of the under surface is much more easily
penetrated than the upper surface, which is covered
with the cuticle of an epidermis, that rests on closely

^ Weismann, Essays on Heredity, vol. i p. 95.

Evolution of Galls. xxxv

packed palisade cells ; the lower surface is consequently
the situation most in favour.

Whatever form the gall takes, the potentialities of
the tissue-growth exhibited by it, must be present at
the spot pricked by the fly. It is not necessary to
assume, with De Vries, that every vegetable cell contains
the potentialities of every other cell in a latent condition.
The conical growing point in every bud contains the
germ-plasm of the next shoot, and consequently of the
whole plant.

The potentialities of growth being present, they are
called into activity by the larva, a result advantageous
to the larva and sometimes described as disinterested
and self-sacrificing on the part of the plant \ We
have just seen that, so far as the larva is concerned,
the peculiar structures of the gall owe their origin
to their success in feeding and defending it ; and so far
as the plant is concerned, these structures have been
evolved in consequence of their value in enabling the
plant to repair injuries in general, and the injuries
inflicted by larvae in particular. If John Doe raises
a cane to strike Richard Roe, and Richard throws
up his arms intuitively to parry the stroke, the action
does not indicate a prophetic arrangement of molecules
to frustrate John in particular, but an inherited action
of defence. The first act of an injured plant is to

* St. George Mivart, Nature, Nov. 14, i88g. ' Now surely it is too
much to ask us to believe that the germ-plasm of the plant, in the
first instance, before even, say, a single cynips had visited it, had in
the complex collocation of its molecules, an arrangement such as
would compel the plant which was to grow from it, to grow those
cells and form a gall.' And in a note he adds : ' It would be very
interesting to know how natural selection could have caused this
plant to perform actions which, if not self-sacrificing (and there must
be some expenditure of energy), are at least so disinterested.'

C 2

xxxvi Introduction.

throw out a blastem, and only those larvae survive
to hand down their art, which emerge from an egg
so cunningly placed as to excite the growth of a nu-
tritive blastem. It is not always possible to keep
the besiegers from using the waters of the moat, although
there is no disinterested thought of the besiegers'
wants when the ditches are planned. So in the war-
game that goes on between insect and plant, natural
selection directs the moves of both players, but there
is nothing generous or altruistic on either side.

The means of defence against parasites which have
been evolved by galls are many of them very curious.
Aphilotrix Sieboldi and some others^ secrete a sweet
glutinous secretion which, like honey dew, is particu-
larly attractive to ants, and leads them to act as senti-
nels in guarding the galls from parasites. Occasionally
ants will go so far as to cover the secreting galls over
with a concrete made of sand, leaving only a tunnel by
which they pass up to reach the stores of honey dew.

A glutinous secretion is sometimes found on long
tufts of hair growing from the gall. A defence of this
kind is used by Andriciis ramuli, and forms a stockade
which entangles parasites before they reach the gall.

A layer of thick-walled parenchyma affords a protection
to some larvae, such as Dryophanta longiventris ; in
others a thick layer of spongy parenchyma, as in Teras
ierminalis, serves the same purpose ; in Cynips Kollari
both these layers are present ; and in addition, these and
many other galls, have an inner gall of stony hardness
which guards the larva like a shirt of mail.

1 Cynips glutinosa glues small insects to the gall ; and a sweet
secretion is found on Cynips calycis, growing on Q. pedunculata.
Giraud, Verh. z.-b. Ges. zii Wien, 1859 ; Dr. E. Rathay, Nature, vol. xlv.
p. 546, 1892.

Defensive Characters. xxxvii

Great size, as in Aphilotrix radicis, occasionally puts
the larva beyond the reach of the parasite, while the
very opposite condition protects by insignificance.
Another effective protection is found in Andricits ciir-
vator, where the inner gall lies in a large hollow
chamber, an arrangement which makes the work of
the parasite difficult and uncertain.

Outside enemies such as tits, pheasants, and squirrels
are as much to be feared as parasites. The larvae are
defended from these, sometimes by the nature of the
outer gall, which in Aphilatrix fecundatrix consists of
closely imbricated scales resembling a hop strobile.
In A. Sieboldi the outer gall is hard and stony ; in
Cynips Kollari and Trigonaspis crustalis, the tannin
which is contained in the tissues renders them dis-
tasteful. As the galls mature the percentage of tannin
becomes less, but the hardening of the epidermic
layers which then takes place affords a new line of
defence. After the gall has fallen another set of influ-
ences secure its safety by the changes they produce in
its surface-colouring. The galls of Andricus ostreus,
Biorhtza renuni, and many others, are supplied, as
Beyerinck has pointed out, with certain hydrocarbon
compounds, which absorb moisture and undergo mole-
cular changes after they reach the ground ; with these
chemical changes the growth of the larva and the devel-
opment of protective coloration in the gall take place.

Cymps Kollari, Dryopliania scutellaris, and a few other
gall-larvae and gall-flies, have the power of emitting
a disagreeable bug-like odour, which is not sexual,
since agamous species possess it, but probably protects
the flies to some extent from birds. Certain galls have
a fruity and aromatic smell ', the use of which does not
' Paszlavszky, IVicn. Ent. Zcit., 1883. p. 130.

C3

xxxviii Introduction.

seem quite clear, unless they can be swallowed and
voided undigested by a temporary host.

It is remarkable that characters, closely resembling
those acquired by fruits, should have been evolved from
a totally different cause. In the case of fruits these
characters have been of service in securing the dis-
tribution of the seeds ; in the case of galls, in securing
the safety of the larvae ; but in both cases it has been
their fitness that has brought them into existence.

Darwin and all writers before him held that the force
calling out gall formation was due to a chemical
secretion injected by the gall-mother. Malpighi con-
sidered that it acted as a ferment on juices existing in
the plant ; and this was the view of Reaumur, but he
added to it the thermal effect of the egg, and the nature
and character of the wound, which varies according to the
shape of the ovipositor of each species. Dr. Derham
thought the formation was * partly due to the act of the
plant, and partly to some virulency in the juice or egg, or
both, reposited on the vegetable by the parent animal;
and just as this virulency is various according to the dif-
ference of its animal, so is the form and texture of the gall
excited thereby.' Darwin speaks of galls as produced ' by
a minute atom of the poison of a gall-insect/ and com-
pares them to the specific local processes of zymotic
diseases. Sir James Paget, writing in 1880, said that 'the
most reasonable, if not the only reasonable theory, is
that each insect infects or inoculates the leaf or other
structure of the chosen plant with a poison peculiar to
itself.' This may be taken as the view accepted by
scientists^ until in the following pages Dr. Adler showed
conclusively that there was no foundation for supposing

' See ' Galls,' Encyclop. Briiann. ed. 9, where the same view is
expressed.

Excitatory Emanations. xxxix

that the gall-mother injected any irritating secretion
whatever, and Beyerinck ' proved that the fluid ejected
by the gall-fly is without taste or smell, and absolutely
unirritating if injected under the skin. It is probably
nothing more than a very mild antiseptic dressing
applied to the wound made in the plant. Both these
authors show plainly that it is not in the gall-mother,
but in the larva, that we must seek for the cause of
gall-growth; and that it is the nature of the salivary
secretion, and the manner of feeding of the larva,
peculiarities inherited by each species, which give the
characteristic growth to the gall. The fact that some-
times a blastem has actually begun to form before the
egg-shell has ruptured, proves that one of the exciting
causes must be a chemical fluid, secreted by the salivary
glands, and possessing amylolytic and proteolytic
ferments. This fluid is capable of passing through the
cell-walls and producing effects at a distance of several
mm. beyond actual contact with the larva \

The necessity for the continuance of the excitation
during the whole period of gall-growth is shown by its
cessation when the larva has perished by parasites.
In some galls, however, the parasites are evolving the
power of prolonging gall-growth beyond the death of
the gall-maker, although they have not yet actually
acquired the art of initiating it.

The duration of gall-vitality is shortest in succulent
galls, such as Spathegaster baccarum, S. albtpes, S. tricolor,
and 5". verrucosus, growing from leaves ; or such as
S. Taschenbergi, S. similis, and Trigonaspis crustalis,
growing from dormant buds. Galls which grow within
the leaf substance, like Spathegaster vesicatrix and

' Beyerinck, Uber die ersten Entwickl. einiger Cynipidengallen, p. 179.
" Hoffmeister.

xl Introduction.

Andricus curvator, live as long as those leaves of which
they form part. Aphilotrix fecundatrix and Cynips
Kollari die at the end of the first summer ; Dryophanta
longiventris, Aphilotrix coUaris, A.globuli, A. autumnalis,
and Ncuroterus ostreus, perish during the first winter ;
the spangle-galls and Biorhiza renum live till spring ;
Aphilotrix radicis, A. Sicboldi, and Biorhiza aptera do
not die till the second winter ; while Andricus inflator
may almost be termed perennial, since new oak-buds
are developed upon it in the following year.

DESCRIPTION OF PLATES^

PLATE I.

Fig. I. Galls of Neuroterus lenticularis.

Fig. i". Galls of Spathegaster baccarum, on the leaf and flowering
catkin.

Fig. 2. Galls of Neuroterus laeviusculus.

Fig. 2*. Galls of Spathegaster albipes ( x 2).

Fig. 3. Galls of Neuroterus numismatis, one gall enlarged.

Fig. 3". Galls of Spathegaster vesicatrix, one gall enlarged.

Fig. 4. Galls of Neuroterus fumipennis.

Fig. 4"^. Galls of Spathegaster tricolor.

Fig. 5. Galls of Aphilotrix radicis. One in the fresh state, the other
in section, after maturity.

Fig. 5". Galls of Andricus noduli. One shoot bears the fresh galls,
the other the galls of the previous year.

Fig. 6. Galls of Aphilotrix Sieboldi. On one stem the galls are
fresh, on the other mature and woody.

Fig. 6". Galls of Andricus testaceipes.

Fig. 7. Galls of Aphilotrix corticis. One portion of the bark exhibits
the fresh, the other the mature galls.

Fig. 7*. Galls of Andricus gemmatus, showing the holes through
which the flies have emerged.

Fig. 8. Galls of Aphilotrix globuli. The woody inner gall shown
at maturity.

* The galls were drawn from fresh specimens by Herr O. Peters,
Gottingen.

xlii Description of Plates.

Fig. 8". Galls of Andricus inflator. Section showing the inner gall
chamber.

Fig. 9. Galls of Aphilotrix collaris. Fresh galls shown in the bud
and detached. Mature adherent galls are also shown.

Fig. 9". Galls of Andricus curvator on the leaf and twig. Section
showing the inner gall.

Fig. 10. Galls of Aphilotrix fecundatrix, showing the inner gall
detached.

Fig. 10". Galls of Andricus pilosus ( X3).

PLATE II.

Fig. II. Galls of Aphilotrix callidoma.

Fig. ii''. Galls of Andricus cirratus (natural size and x 3).
Fig. 12. Galls of Aphilotrix Malpighi.
Fig. 12". Galls of Andricus nudus ( X2).

Fig. 13. Galls of Aphilotrix autumnalis, showing the mature gall
detached.

Fig. 13". Galls of Andricus ramuli.
Fig. 14. Galls of Dryophanta scutellaris.

Fig. 14*. Galls of Spathegaster Taschenbergi, at maturity after the
escape of the flies. One fresh gall enlarged.
Fig. 15. Galls of Dryophanta longiventris.

Fig. 15*. Galls of Spathegaster similis. One on the twig, one
showing through the bud, and one enlarged.
Fig. 16. Galls of Dryophanta divisa.

Fig. 16". Galls of Spathegaster verrucosus. One on the leaf and
one on the petiole. One on a leaf, and one escaping from a bud,
enlarged ( X2).

Fig. 17. Galls of Biorhiza aptera. Fresh galls of the first year
(experimentally grown) ; beneath, a mature woody gall.

Fig. i7\ Galls of Teras terminalis ; the lower is a mature gall in
section.

Fig. 18. Galls of Biorhiza renum, with the fly magnified.
Fig. 18*. Galls of Trigonaspis crustalis. Flies, male and female,
magnified.

Fig. 19. Galls of Neuroterus ostreus.
Fig. I9'\ Galls of Spathegaster aprilinus.

Fig. 20. Galls of Aphilotrix seminationis on the leaf and flowering
catkin.

Fig. 21. Galls of Aphilotrix marginalis.
Fig. 22. Galls of Aphilotrix quadrilineatus.
Fig. 23. Galls of Aphilotrix albopunctata.

Description of Plates. xliii

PLATE III.

All the figures in this plate are drawn from photographs. The egg
when accompanying the ovipositor is drawn to the same scale.
Ovipositors belonging to alternating generations bear the same
numbers.

Fig. 1. Ovipositor of Andricus cirratus, X55. The terebra is with-
drawn, that the two plates, the muscles, and the seta, may be more
clearly displayed.

1-5. The five muscles described in the text as moving the

terebra.
h. The posterior plate, v. The anterior plate, b. The arch. c.
The horn. s. The seta. p. The anal papilla, st. The sheath
of the terebra.
Fig. 2. Ovipositor of Neuroterus laeviusculus, with egg ( x 30).
Fig. 2". Ovipositor of Spathegaster albipes, with egg ( X36).
Fig. 3. Ovipositor of Neuroterus fumipennis (X36).
Fig. 4. Ovipositor of Aphilotrix radicis, with egg (X25).
Fig. 4". Ovipositor of Andricus noduH, with egg (X36). The
serrated spiculae are withdrawn.

Fig. 5. Ovipositor of Dryophanta scutellaris, with egg ( X30).
Fig. 5". Ovipositor of Spathegaster Taschenbergi, with egg ( X36\
Fig. 6. Ovipositor of Biorhiza renum (X36).
Fig. 6». Ovipositor of Trigonaspis crustalis ( X30).
Fig. 7. Ovipositor of Teras terminalls ( x3o\

Fig. 8. Egg of Biorhiza aptera taken from the ovary direct ; the
adjoining figure exhibits one with the embryo ( x 200). The egg-
stalk is cut short.

Fig. 9. Egg-tube from the ovary of Neuroterus fumipennis. Three
eggs are seen in the course of formation ( x 100). In the last, which
is the most developed, the formation of the egg-stalk is distinctly
seen.

Fig. ID. Egg of Aphilotrix autumnalis, taken from a bud ten hours
after oviposition ( x 200"). The egg-stalk is shut oif from the egg-cavity.
Its whole length is not shown.

ALTERNATING GENERATIONS

IN

OAK GALL-FLIES

CHAPTER I.

Introduction. — Earlier Views. — First Observations on Alter-
nation OF Generations. — Methods of Investigation.

The curious fact that in many species of oak gall-flies
female specimens alone were found, long attracted
entomologists to a closer study of this interesting
family. But T. von Hartig ^ was the first to demonstrate
by experimental breeding, after having reared many
thousands of flies, that there are numerous species in
which none but females exist; and that these when
they emerge from the gall have their ovaries filled with
perfectly developed eggs, which they at once proceed
to deposit. Although the occurrence of partheno-
genesis in these species had been placed beyond doubt
by these experiments, there was much in the life

* L/bey die Famtlien d. Gallwespen. German's Zeitschr. f. d. Entomol.
1840-43, vol. ii. pp. 176-209; vol. iii. pp. 322-358; vol. iv. pp. 395-422.

B

Q, Earlier Views.

history both of the agamous and of the sexual forms
still left to be elucidated. There was no means by
which this could be done satisfactorily except by direct
experimental breeding. In carrying this out, however,
many, practical difficulties occurred, as constantly
happens in experiments of this nature, and these served
for a long time to delay the solution of the problem ; so
for a season at least it was necessary to rest satisfied
with a provisional explanation which was in reality
little better than a simple hypothesis.

In the year 1861 an entirely new theory was
propounded by Osten-Sacken \ whose investigations
into the history of the numerous species of North
American oak gall-flies are well known to the scientific
world. He believed he had discovered that those
species which had hitherto been considered agamous
were in reality sexual, but that the males were
developed from differently formed galls. If this theory
were correct all that remained to be done was to
discover which were the associated gall-forms. But
further observation did not confirm this view, and
Osten-Sacken had to abandon it.

Some time afterwards, in 1864, Walsh ^, an American
entomologist, advanced a totally different opinion.
Walsh had obtained out of apparently exactly similar
galls, on one occasion individuals of Cynips spongifica
of both sexes, and on another occasion females only, but
of Cynips aciculata which are quite different in form.
Had this observation been correct, and had it been

* Stettiner Entomolog. Zeit. 1861, vol. xxii. pp. 405-423.

* Proceedings of the Entomological Society, Philadelphia, vol. i.

Earlier Views. 3

true that from the same gall there had emerged not
only one male but also two different female forms,
it would have been fatal to the theory of partheno-
genesis in the agamous Cynipidae. All the agamous
species would come at once to be regarded as
dimorphous female forms, and it would only be
necessary to ascertain which were the allied female
forms. It looked as if we had here among the gall-
flies a phenomenon analogous to that which Wallace
had discovered among the Malay Papilionidae, where
females of the sam^e species are found of two or even
three entirely different forms. Walsh's theory, how-
ever, received but little countenance, and in Germany
it was refuted by Reinhard ^ who succeeded in estab-
lishing in the most satisfactory manner that partheno-
genesis undoubtedly did exist among many species
of Cynipidae. After this the subject seems to have
dropped, and I am not aware of any researches, either
in favour of or against the views of Walsh, having
been made for a considerable time. Indeed it was not
until 1873, after Walsh's death, that his fellow-country-
man Bassett ^ published some fresh observations on the
propagation of Cynipidae, of which the most interesting
is the following : — Bassett had repeatedly found
enormous numbers of a gall belonging to a species
of Cynips, on a small oak {Quercus bicolor). These
galls appeared with the leaves, causing shapeless
swellings of the petiole and midrib ; they contained

' Reinhard, ' Die Hypothesen iiber die Fortpflanzungsweise der
eingeschlechtigen Gallwespen,' Berl. Entom. Zeitschr. 1865, \'0l. ix,
^ Canadian Entomol. (May, 1873, vol. v. pp. 91-94).

B 2

4 Earlier Views.

a large number of larvae, and in June there emerged
flies of each sex in nearly equal proportion. Late in
the summer there was formed on the points of the
young shoots of the same oak tree, a differently shaped
gall in which the flies passed the winter. This latter
species occurred in the female sex only. It closely
resembled the former species, but was somewhat larger.
From this observation Bassett arrived at the conclusion
that each species of Cynips which is found occurring
exclusively in the female sex is succeeded by another
generation which is bisexual : and this he contended
was entirely opposed to Walsh's hypothesis. Bassett
concluded by saying that it would not surprise him
if it were proved that every species of the genus
Cynips had each year two generations differing in the
manner indicated by him. Had I been acquainted
with Bassett's work in the year 1875, when I began to
investigate the Cynipidae more carefully, I should
probably more easily have found the key to the
mysterious problem of their propagation. A lucky
chance led me to select the species of Neuroterus for
my first experiments : these galls are easily collected in
large numbers, and there is little difficulty in rearing
the flies. In every case I made a point of breeding
the flies from the galls, so that I might be absolutely
certain of the species. The flies emerge in March and
April from Nciirotcriis galls which had matured in
autumn, and they proceed at once to lay their eggs in
the buds of the oak. It struck me as remarkable that
although the ^^% was laid so early, the gall did not
develop until July : and it was the strangeness of this

First Experiments. 5

circumstance, added to a desire to investigate the
method of gall formation, that led me to undertake my
first direct experiments in breeding. These afforded me
the surprising result that from the eggs laid by Neuroterus
there appeared a totally different generation, one so wholly
tinlike its parent that it had been described hitherto as of
another genus (Spafliegaster). This fact was published
by me in 1877 \ and what Bassett had only thrown
out as a conjecture in 1873 was now proved and
demonstrated in one species at least. It is not then
correct to affirm that Walsh had previously discovered
this alternation of generations. Walsh had only
broached the theory that to one male form might
belong two entirely different female forms which had
until then been described as distinct species : but it is
clear that the alternation of generations in the Cynipidae,
as discovered by me, had nothing whatever in common
vv'ith Walsh's supposed dimorphism. After I had once
discovered this remarkable alternation of generations in
Neuroterus it was interesting to investigate the propaga-
tion of the remaining genera and species. The fauna
of this locality (Schleswig) includes about forty species,
and this fairly represents the oak gall-flies of North
Germany ; to these therefore I steadily extended my
observations. But before I go into any account of
these species in detail, it may be well first to describe
shortly the method which I adopted in carrying out my
experiments.

In order that the results which I obtained might
be unquestionable it was necessary to select a method

^ Deutsche Entomolog. Zeitschr. i8t], Heft I.

6 First Experiments.

which provided against every possible source of error.
This could only be satisfactorily accomplished by
watching the development of the gall of each species,
from the time when the egg was laid until the gall
reached maturity. Unfortunately, however, this peculiar
difficulty exists, that the most important phase of de-
velopment, viz. that during which the eggs of the fly are
buried in the bud or tissues of the oak, must unavoid-
ably be hidden from direct observation. Indirect
observation alone is available, for any actual examina-
tion of the eggs when laid must necessarily end in
their destruction. Thus if a gallfly lays its egg in
a bud, one can predict with certainty what gall will be
produced, so long as care is taken that the same bud is
not pricked either before or afterwards by another fly.
Breeding experiments must therefore be so arranged
as to enable each species to be isolated and watched
while actually depositing the egg,.

For this purpose I had a quantity of little oak trees
planted in numbered pots, each pot serving for experi-
ments with flies of the same species. The experiments
were made in a room, and the flies were carefully
watched from the time they were placed upon the tree
until they began to prick the buds : those buds which
had been undoubtedly pricked were then marked by
means of a thread tied around them. It was naturally
impossible to go on watching the flies for many hours
together, and I adopted the plan of covering the trees
over : in this way flies placed on the trees were pre-
vented from escaping, and at the same time those of
other species were kept away. At first I used glass

Methods of Investigation, 7

protectors, but afterwards I found covers made of gauze
and provided with a glass top were more suitable : they
can easily be made of any size, are convenient for
observation, and allow of free ventilation ; besides
under them a tree can be watched for days together,
whereas a bell-glass protector soon becomes dimmed
with moisture and requires frequent cleaning.

The oak saplings I have sometimes grown and some-
times obtained from nurserymen. The four to six year
old saplings are to my mind the most convenient size,
and a large choice of them makes experimental breeding
much more easy. I employed almost entirely Quercus
sessiliflora. It is essential that a sapling about to be
used in an experiment should have its buds well
developed, as these are always preferred by the flies.
There is a difficulty in rearing species which only
prick flower-buds, since young saplings which do not
produce flowering catkins are useless for the purpose.
The only way to rear those species is to make the
experiments on full-grown trees in the open air,
taking every means to guard against possible error \
On the other hand it is very easy to make experiments
on saplings with species which prick the leaves or
bark. Such briefly was the plan adopted by me in
investigating the development of the species which
I am about to describe.

As it is very difficult, and in some cases almost
impossible, to distinguish the flies of nearly related
species from each other, any illustrations of the insects

[^ Dr. Beyerinck used for this purpose cubes of wire covered with
muslin and tied round the branch.]

8 Methods of Investigation.

themselves would be practically useless. But all the
species can be distinguished without difficulty by means
of their galls, and these have been drawn as faithfully
as possible from fresh typical examples. The galls of
associated generations have been marked in the plates
by the same number, the generation occurring only in
the female sex being marked thus, ' i,' and that in
which both sexes occur thus, * i^ '.

For greater convenience of reference, I have
arranged the species in the following groups : —

I. Neuroterus.
II, Aphilotrix.

III. Dryophanta.

IV, BlORHIZA,

CHAPTER II.

Description of the Species of Cynipidae observed, with a view
TO determining their Alternation of Generations.

I. Neuroterus Group ^

1. Neuroterus lenticularis. 01."

Gall. The gall appears on the under surface of the
oak leaf, and occurs frequently in large numbers, forty
to fifty on one leaf. It is circular, 4-6 mm. in diameter;
the under surface which is in contact with the leaf is
smooth and flattened, and of a whitish colour; the upper
surface has a slightly conical prominence in the centre,
and is of a pale yellow or reddish colour with brown
stellar hairs. The galls appear in July, mature in
September, and fall to the ground at the end of
September or beginning of October. (Fig. i.)

Rearing the Fly. The mature galls are collected at
the time when they begin to detach themselves from
the leaves. The larva, which may be seen lying in
a small cavity in the centre of the gall, is still very
minute and requires a certain degree of moisture for
its further development. The galls should therefore be

[1 Neuroterus, Hartig; Spathegaster, Hartig ; Anicristus, Foerster;
Manderstjernia, Radoszkowsky.

^ Cynips lenticularis, Olivier ; Neuroterus Malpighii, Hartig, Tasch.,
Thorns.]

lo Observations on Cynipidae.

laid on damp sand, but the airiest possible situation
must be chosen, to avoid mildew. If the galls are kept
in a room, the larvae develop much more quickly than
they do in the open air, in consequence of the higher
temperature, and in the course of about four weeks
they are fully grown. Then if the galls are prevented
from shrivelling, by keeping them on damp sand or
over water, the first flies may be obtained in about four
weeks more. In this way I have hatched flies in
November and December, but it was soon apparent
that these premature specimens were little fitted for
experimental breeding. They were much weaker and
more puny than those developed under natural con-
ditions, and it is consequently preferable to leave the
galls to pass the winter in the open air. This may
very simply be done in the following way. Half fill
a flower-pot with earth or sand, spread the galls upon
this, and cover them over with a layer of moss. Then
for greater protection tie a piece of gauze firmly over
and plunge the pot up to its rim in the ground. This
method of wintering is to be recommended for all galls,
as they are thus placed under natural conditions, and it
is certain that the development of the flies is left to
follow its normal course. In this experiment the flies
emerged mostly in April, but a few not until May. For
this variation in the time of their appearance I believe
that temperature is alone responsible.

Fly. Size 2-5-3 mm. Colour black ; thorax dull,
rough and finely punctate; abdomen shining; almost
round when looked at from the side, somewhat com-
pressed. Legs lighter ; of a brownish red colour,

Neuroterus lenticular is. ii

except the coxae and the base of the femora which are
brown. The antennae are fifteen jointed, the first two
joints being yellowish.

Experimental breeding. My earliest attempts at
breeding on a large scale were made in 1875 with
Neuroterus lenticularis. These experiments are easy
enough with this species if only a sufficient number
of flies are available. As soon as they leave the gall
they begin to deposit their eggs in the oak buds.

It had hitherto been taken for granted that this species
produced a gall resembling that from which it emerged ;
many points nevertheless remained obscure and puzzling.
It had been long known for example that the gall of
Neuroterus lenticularis did not appear until July, but as
the eggs were deposited by the flies in April, three
months must have passed away before any trace of gall
formation had become visible. It was assumed therefore
that the embryonic development of the larva demanded
this lengthened period ; and this was quite possible,
since other species seemed to require an incubation of
even longer duration. For example Andricus curvator
emerges in June and lives for two or three weeks during
which it lays its eggs, but the galls do not appear
until early in the following year. This could only be
explained by supposing that the egg remained dormant
during the winter, and did not develop until next spring,
as is known to be the case with the eggs of many butter-
flies. The three months' egg-rest of Neuroterus lenticu-
laris therefore was not unprecedented. More conclusive
evidence in support of this supposition was wanting ;
but even if it were correct it failed to explain another

12 Observations on Cynipiaae.

phenomenon. We sometimes find on a single oak leaf
from loo to 150 Neurotcrus galls, therefore there must
have been the enormous number of 100 to 150 eggs laid
in a single bud ; and these eggs must have been
accurately deposited on the rudimentary leaf while it
was yet folded in the bud. This was a supposition
that seemed very improbable.

My breeding experiments soon threw a flood of light
on these apparently mysterious phenomena.

In the year 1875, as soon as a sufficient number of
flies had emerged from the galls, I began in March to
place them on the oak saplings and watched to see them
prick the buds, I was soon able to satisfy myself as to
how a fly proceeds when it deposits its eggs. It first
examines the buds carefully with its antennae until it
finds one that suits it, when it takes up a different
position. It advances towards the apex of the bud and
pushes its ovipositor down under one of the bud-scales.
After several attempts the ovipositor is forced in and
glides down under the bud scales to the base of the bud-
axis which it penetrates from without inwards. This
can only be accomplished by imparting to the ovipositor
a direction at an obtuse or right angle to the course it
followed when entering. The natural curvature of the
ovipositor here stands the fly in good stead, but it
requires a vast expenditure of time and strength before
it can penetrate the heart of the bud. In order to
investigate satisfactorily the various steps constituting
the act of ovipositing, it is a good plan to fix the fly in
the very act by dipping it into chloroform or ether.
During my experiments in 1875 one oak sapling had

Neuroterus lenticularis. 13

thirty-four buds pricked between March 28 and April 6.
Of these buds only nineteen developed, and as they
unfolded and their leaves became visible I examined
their surfaces with the greatest care for any sign of the
eggs which had been deposited in the bud. I was at
first unsuccessful, but after a long search I discovered
at last five of the young shoots exhibiting traces of gall
formation on their leaves. They were small round
excrescences, rich in sap, which grew tolerably quickly,
and were soon recognizable as the galls oi Spathegastcr
baccarum.

Thus in spite of taking every precaution to ensure
that the buds were pricked by Neuroterus lenticularis,
a perfectly different gall had been formed from the one
out of which this Neuroterus had emerged. I did not
rest satisfied with this one attempt, but continued for
many years to make experiments with this and many
other species of Neuroterus.

It is remarkable in experimental breeding how small
is the number of galls that actually develop compared
with that of the eggs deposited in the buds. Many of
the buds themselves come to nothing, but even in those
which grow there are a great number in which the galls
do not form. For example in 1877 I made an experi-
ment in which the results were particularly unfavourable.
An oak was pricked abundantly by Neuroterus lenticu-
laris, and yet only a single Spathegaster baccarum gall
was formed. In such experiments it very probably
happens that the conditions of life natural to the flies
have not been successfully reproduced, and consequently
many of the eggs laid fail to develop. I have, however,

14 Obseruaiions on Cynipidae,

observed the same thing happen wheh oaks growing in
the open air have been pricked, and I am therefore
compelled to attribute to meteorological conditions
a most important influence over the development of the
egg. The appearance of the flies almost always takes
place about the same time, and embryonic development
begins immediately after the eggs are laid. Absolute
rest in the evolution of the egg never occurs, for even if
the temperature should be very low the formation of
the blastoderm begins at once. Naturally this proceeds
more slowly in a cold than in a warm season. I have
satisfied myself by various experiments that when
pricked buds are kept in a warm room the several
stages of embryonic development run their course
much more quickly than they do in buds kept in the
open air. In any case the embryo reaches its full
development in a few weeks. It may happen, however,
that at the particular time when this takes place vegeta-
tion may be backward, and the circulation of the sap
may not yet have begun in the tree, nevertheless the
time when the development of the embryo is completed
is just the time when gall formation should make
a beginning. As long as the embryonic envelopes
remain intact gall formation does not begin, but it starts
the moment the larva frees itself from the egg coverings.
Around the larva cell proliferation now commences and
this corresponds to the first beginning of gall formation.
But the production of this cell proliferation is con-
ditional, and depends on the state of vegetable growth ;
the sap, the pabulum of which the cells are formed,
must be in circulation. When cold weather retards

Spathegaster baccarum. 15

vegetation so that the bud gets little or no nutritive
material, gall formation cannot begin and the larva
perishes. Accordingly we find in a cold and late
Spring the galls of those flies which prick buds early
are very sparingly found. It happened, for example,
that the Spring of 1877 '^^^^'^ cold and very late, and the
early galls were unusually scarce. This interfered
with experimental breeding and made my investigations
exceptionally difficult. If in every case where a bud had
been pricked by a gall-fly, a gall could be unfailingly
collected, then it would be easy to prove the succession
of the several generations ; unfortunately, however,
many of these experiments fail.

In order if possible to guard against this, I had the
oaks which had been pricked brought into a warmer
room, so as to force them to shoot ; but even then
I was scarcely more successful. In some species cer-
tainly the development of the galls was hastened, but in
others on the contrary the results were negative only.

[The Common Spangle is found on Quercus pedunculata, Q. sessili-
Jlora, and Q. pnbescens.

Inquiline. Synergtts Tscheki in April.

Parasites. Eurytoma sigitaia, Torymus auraius, T. hiberna»s,
T. sodalis, Syntomaspis fasfitosus, S. candata, Pleurotropis rosarttm,
in May. Pteromalns dissecfus, P. tibialis, Decatovna bigntiata, Peso-
ntachus gallarum, Pleurotropis sosarmus, Entedon flavoniaculaia, and
Megasiigmus dorsalis.']

P. Spathegaster baccarum \ L.
Gall. Spherical, 3-5 mm. in diameter ; of a greenish
colour, often studded with small red spots ; of soft,

[' Cytiips quercus- baccarum, Lin. ; Spathegaster interrupter, Hartig ;
Neuroterus lentiatlaris, sexual form, Cameron ; Neuroterus baccarum,
Mayr.]

i6 Observations on Cynipidae.

sappy consistence ; the gall grows through the leaf,
its larger segment projecting from the lower surface
of the leaf. This gall not only occurs on the leaves
but is found also on the peduncles of the male
catkin, and is then smaller and of a pale reddish
colour. (Fig. i^)

Ply. Size, 3-5 mm. ; of a black colour ; thorax dull,
slightly rough ; legs and coxae yellow, as also the basal
segments of the antennae. Abdomen distinctly pedun-
culate. The male has fifteen, the female fourteen joints
to the antennae. The wings are long, broader towards
the tip, and longer than the body.

Rearing the Ply. The fly emerges from th? begin-
ning to the middle of June. Owing to the sappy
nature of the galls it is not wise to collect them too long
before the flight time of the fly, otherwise it is difficult
to prevent the galls from shrivelling and drying. In
order to hatch the flies satisfactorily it is absolutely
essential to keep the galls fresh : it is scarcely possible
to do this for longer than eight days in closed tin or
glass vessels. Since these flies occur in both sexes it
is necessary to see that they copulate before ovipositing.
I have been in the habit of spreading the galls out on
damp sand as I collected them, and placing over them
a gauze covering. The males are usually the first to
appear, and as soon as the females emerge fecundation
takes place, but generally too rapidly for this to be
actually observed. To demonstrate that it has occurred
it is necessary to prepare the rcceptaciila semtnts of some
of the females for microscopical examination. If these
are found filled with spermatozoa it may be taken as

Spathegaster baccarnm. 17

probable that most of the females of the brood have
been fertilized, and breeding experiments may be
proceeded with.

The female flies are then placed on oak saplings, care
being taken that the leaves are tender and in actual
growth, as it is only in that condition that they can be
pricked. Unless leaves in this state can be provided,
no results need be expected.

I made my first observations on ovipositing in Spathe-
gaster baccarum in the open air. In the year 1875,
from June 18 to 21, I watched many of the females
creeping about on the tender oak leaves and pricking
them on the under surface. Having marked the pricked
leaves by tying a thread around the leaf-stalk, I waited
for the development of the galls. In about three weeks
the beginning of gall formation was observable, and the
galls could soon be recognized as those of Neuroterus
lenticularis.

In June, 1876, I placed flies, reared by myself, on an
oak sapling and repeated this same experiment under
more exact control. Two leaves were pricked, and at
the end of twenty days I recognized the first beginning
of gall formation, and the galls again proved to be
those of Neuroterus lenticularis.

Now the mystery was completely solved, and I had
discovered what became of the eggs laid in the buds by
Neuroterus lenticularis, and why the galls appearing in
July are found in such numbers on a single leaf.

[The currant gall is found in May on Qttcrctis pednncidata,
Q. sessiltflora, and Q. pubescens.

Inquilines. Synergus albipes in May and June. S. facialis and
S. radiatus in June. 5. apicalis, S. ntficomis, S. thaumacera.

C

1 8 Observations on Cynipidae.

Parasites. Toryums abdoniinalis, T. incertus, T. regius, and
T. auratus in May and June. Ewytoma rosae and Pteromalns imniacu-
latus in July. Tetrastichus atrocaeruleus, Eupelmus annulatus, and
according to Barrett the Tortrix, Zeiraphera coutmtmaiia.']

2. Neuroterus laeviusculus. Schenck \

Gall. Cup-shaped, the edges thinned and incurved ;
in the centre there is a small but distinct boss sur-
rounded by a circle of brownish hairs ; diameter
2-3 mm. The form of the gall is often irregular, the
rim bent ; colour pale or reddish. The gall appears in
July and matures in September. (Fig. 2 ^.)

Rearing the Fly. When the mature gall falls from
the leaf, its under surface will be found to be distinctly
swollen. In order to observe the development of the
flies indoors the galls must be kept on damp sand.
Their progress may be forced, and in a room they will
emerge in November, but in the natural course they do
not appear until March of the following year. The
earliest date on which I have found them in the open
air was March 9.

Ply. Size, 2-4 mm. ; black ; thorax smooth and
shining; abdomen much compressed, elongate; legs
distinctly paler, white or yellowish, coxae and base of
femora dark.

Experimental breeding. I have made experiments
in breeding with Neuroterus laeviusculus in the same

[1 Neiiroferus pezizaeformis, Schtdl.]

^ This gall is frequently confused with that of Neuroterus fitmu
pennis. I myself made this mistake, and in my earlier publications
these two names must therefore be transposed, but the facts remain
unaffected.

Spathegaster albipes. 19

way as with the former species, and have frequently
succeeded in getting the flies to prick the small oaks.
The first accurate experiments were made in March,
1875. Between March 14 and 26, thirty-six buds in
all were pricked by a large number of flies. On the
unfolding leaves there appeared in May the gall of
a totally different fly, Spathegaster albipes. From the
strict control exercised there could be no doubt that
these galls proceeded from Neuroterus laeviusculus.
From my first experiment I obtained thirty-six galls,
but from others made in 1877 I only got two galls. As
a rule experiments made with these flies are pretty
certain to succeed.

[The smooth spangle gall is found on Q. pedunculaia.
Inquiline. Synergus Tscheki in April.

Parasites. Torynttis sodalis in March and April. T. hibernans.
The spangle galls live about nine months.]

2^. Spathegaster albipes. Schenck\

Gall. Size, 1-2 mm. in length; oval with a short apical
point, of a greenish yellow colour, smooth or thinly set
with solitary hairs. The galls are sessile on the leaves,
which they deform more or less, causing indentations or
sinuosities and often stunting them in their growth.
This is due to the mode of origin of the gall which is
formed on the rudimentary leaf while yet in the bud.
The area occupied by the gall in the bud is of course
small, but the effect upon the leaf when it expands is
much more marked. (Fig. 2^.)

Fly. Size, 1-2 mm. long ; black ; thorax smooth

\} Neuroterus laeviusculus, sexual form, Cameron. Neuroterus albipes
Mayr.]

C 2

30 Observations on Cyniptdae.

and shining; abdomen distinctly pedunculate. Legs

pale, only the coxae and bases of the femora dark.

The flies emerge at the end of May or beginning of

June.

Experimental breeding. I observed these flies for

the first time on June 3, 1875, while they were busy in

the open air pricking the under sides of the tender oak

leaves. They are very delicate little flies, and can only

be kept alive for a few days, but it is not difficult to

observe them ovipositing if they are provided with very

tender leaves. They are first seen to move about

actively and examine the under surface of the leaves

carefully with their antennae. They then direct the

point of the abdomen perpendicularly to the surface of

the leaf, the terebra is pushed into it, and an ^^^ glides

down into the channel thus pierced. This fly can

deposit a large number of eggs in the leaf in a short

space of time. The first traces of gall formation are

found at the end of three weeks as little hairy spots

which soon develop into the galls oi Neurotcrus lacvius-

culus. Of these there may be as many as 200 on

a single leaf.

[Schenck's gall is found in May on Quercus sessiliflora and Q. pedun-
culata,

Inquiline. Synergus apicalis.'\

3. Neuroterus numismatis \ 01.

Gall. Very pretty circular galls, like buttons

covered with brown silk, with a shallow depression in

the middle. Diameter, 2 mm. They mature in the

autumn with the preceding {Neuroterus) gall. (Fig. 3.)

\} Cynips numismatis, Oliv. Neuroterus Reaumuri, Hartig.]

Spathegaster vesicatrix. 21

The flies are reared in exactly the same way as
Neuroterus lenticular is.

Fly. 2-5 mm. in length ; black ; thorax dull, finely
punctate ; scutellum somewhat closely haired. The
colouring of the legs variable, yellowish brown, bases
of the femora mostly dark. Abdomen, looked at from
the side, almost round ; basal joints of the antennae
dark, which is the only character by which this fly is
distinguished from Neuroterus lenticularis.

Experimental breeding. Experiments, in the manner
described above, were also made with this fly, the first
being in March, 1875. From this first attempt, in which
thirty-two buds were pricked, I obtained in all five
galls which were formed under the leaf surface and
proved to be those of Spathegaster vesicatrix. In 1876,
I repeated the experiment with the same result. Later
also an English entomologist Fletcher ^ obtained from
similar experiments the same species oi Spathegaster.

[The silk button spangle galls appear in July on Quercus sessiliflora,
Q. pedtinculata, and Q. pubescens.

Inquiline. Syttergns Tscheki, March to June.

Parasites. Torynms ntutabilis, June — August, T. inconstans, T.
fusckrux, T. geranii in July. Platymesopus tibialis in June. Eurytoma
curta,E. aethiops. Pieromalitsdomesticus in ]uly. Eupelmtts urozonus.
Pleurotropus sosamtus.']

3**. Spathegaster vesicatrix. Schltdl.^

Gall, These galls are inconspicuous and are em-
bedded in the substance of the leaf, which they resemble.
They project only slightly above the level of the surface.

^ J. E. Fletcher, Entont. Month. Mag., vol. xiv. p. 265 (May, 1878).
\^ Ncuroto-us fiumismatis, sexual form, Cameron, Neuroterus
vesicatrix, Mayr.]

22 Observatmis on Cynipidae.

Each bears in its centre a little conical projection from
which ra3's run out to the margin of the gall. (Fig. 3".)

The flies emerge in June, and are very easily reared
if the galls are collected shortly before they mature.

Fly. Size, 2 mm. ; black ; thorax shining ; legs
yellowish, coxae and bases of femora dark. Male and
female similar.

Experimental breeding. As it is very difficult to
collect the flies of this species in large quantity, I have
only once been able to make an experiment in breeding,
and that was in the open air. On June 20, 1875,
I observed several females creeping about on the
under surface of the oak leaves and laying their eggs.
I marked eight leaves which had been pricked, by tying
threads upon them. After three or four weeks small
round galls appeared which proved to be those of
Neuroterus nimiismatis.

[The blister-gall occurs in May on Qnercus sessiUJlora and Q. pedun-
culata. A different but similar gall appears on Q. pitbescens and
Q. cerris.

Inquiline. S'p.l oi Synergits.

Parasites. Sp. ? of Torymus. This gall continues to live after its
gall-maker has emerged.]

4. Neuroterus fumipennis. Htg.^

Gall. Generally circular, with the edges often in-
curved and emarginate. The gall is of a pale or reddish
colour with delicate brown stellar hairs. (Fig. 4.)

This gall has a certain resemblance to that of
Neuroterus lenticiilaris, but has more frequently been

[• Spathegaster varius, Schenck.]

Neuroterus fumipennis. 23

mistaken ior Neuroterus laeviusculiis. Indeed, as I have
already said, I myself at the outset confounded laevius-
culiis v^\\h fumipennis.

Rearing the Fly. The galls are collected when they
mature in the beginning of October, and are preserved
through the winter in the same way as Neuroterus
lenticularis. In one point however they differ essentially ;
in lenticularis the development of the larva begins and
continues without intermission from the time the galls
fall to the ground, but in fumipennis on the contrary
there is a complete winter rest. If a gall oi fumipennis
be opened in the month of March, the larva will be
found to be absolutely at the same point of development
that it had reached in the autumn ; whereas in the
other Neuroterus galls the larva is by that time fully
grown or has even assumed the pupa-state. It is only
during the month of March that larval development
ht^vci^'vafumipenniSf towards the end of April it becomes
a pupa, and the perfect insect appears in May. But the
actual date of its appearance varies from two to three
weeks according to the temperature. It is not possible
with this species, as with the others, to hasten the
development of the larva by keeping the galls in a warm
room during the winter months.

Fly. This fly is easily distinguished from all the
other species of Neuroterus. Size, 2 mm. ; thorax dull,
black ; base of abdomen orange ; legs, including the
femora, orange ; wings, especially at the tips, smoky.

Experimental breeding. When the fly makes its
first appearance in May it finds the oak buds already
well developed and beginning to swell, while the scales

24 Observations on Cynipidae.

are becoming less tightly imbricated. It is thus com-
paratively easy for it to insert its terebra into the bud.
I made my first experiments in May, 1875, and I re-
peated them in May, 1876. They are very active little
flies, and in this respect differ from the former
species ; they are continually running from side to
side and flying from one shoot to another. When the
buds begin to loosen, they are able without much effort
to insert their terebra and deposit their ^gg. It often
happens that several eggs are deposited on the same
leaf, while later we find from three to five galls grow-
ing there, and the leaf distorted and puckered. The
gall produced by this species is that of Spathcgaster
tricolor.

[The cupped spangle gall is found in August on Qtterais pedun-
culata and Q. sessiliflora ; occasionall}^ on the upper surface of the leaf
Inquiline. Synergus Tscheki in March of second year.
Parasite. Torymns sodalis.'\

4*. Spathegaster tricolor. Htg.^
Gall. Soft and sappy ; of a pure white or slightly
greenish yellow colour ; round, somewhat flattened at
the summit, covered with simple upright white hairs,
which usually fall off when the gall is mature, and it is
then liable to be confused with Spathegaster baccarum.

(Fig. 4^)

The gall does not mature until July, and the fly
emerges from the beginning to the middle of July.

Fly. Size, 2 mm. ; black ; thorax slightly shining,
somewhat punctate; legs reddish yellow; abdomen
dark brown, reddish yellow at the base ; wings cloudy,

[^ Nettrotenis tricolor, Maj'r.]

Spathegaster tricolor. 25

particularly at the tips ; basal joints of the antennae
pale ; male and female similar.

Experimental breeding. I made, in 1875, some ob-
ser\'ations on the manner in which this species pricks
the buds. On July 17 I found several females busil}^
hunting about on the under surfaces of the oak leaves
which they finally began to prick, and during the month
of August the galls of N euroteriis fiimipennis developed
on the pricked leaves. I have not made any further
experiments with this species.

[The hairy pea gall is found in June on Quercus pednnculata and
Q. sesstliflora.

Inquilines. Synergns albipes, S. facialis, and S. thanmacera all in
June and July.

Parasites. Eurytoma rosae and species of Totymus and Pteromahis
in July. This gall is often found on Lammas shoots.]

The Ncuroterns and Spathegaster forms just de-
scribed had formerly been considered as belonging to
different genera, because it was not known that they
were alternate generations of the same insect. This
view was perfectly justifiable since very important
differences exist between the two generations. A com-
parison of the galls of the two generations would not
lead us to associate the two species with each other, for
the difference between them is often much greater than
between two wholly distinct species, such as Neuroterus
lenficularis and Neuroterus numismatis. I will refer
later to the important distinction that the flies in the
one generation belong to both sexes, and in the other
exclusively to the female sex. The parthenogenetic
propagation of Neuroterus is constant, and is now so
satisfactorily established that it requires no further proof.

26 Observatio7is on Cynipidae.

If we compare the flies of the two generations
belonging to any of the species above described, we
shall find the differences at first sight very slight. The
difference of colouring is unimportant, and is chiefly
observable in a slight variation in the colour of the legs ;
nor is the size of the body very different, while the
form and surface markings agree in many points. At
the same time it is not difficult to distinguish the one
generation from the other, indeed if the two were placed
side by side it would be difficult to mistake them,
their bodily conformation being totally different. The
Neuroterus is more compressed, the abdomen much
more developed, the wings shorter than the length of
the body, the antennae about two-thirds of the latter.
The Spathegaster, on the contrary, is more slender,
has longer and narrower wings, which always exceed
the length of the body ; the antennae are somewhat
less than two-thirds of the length of the body; and
lastly the abdomen is not so strongly developed.
The configuration and size of the abdomen depend
entirely on the size and form of the ovipositor.
When the ovipositor is of great length, as in Neuro-
terus laeviiisculus, it lies in repose spirally coiled in
the abdominal cavity; and from the greater space
which such an ovipositor requires, a larger abdomen
becomes necessary. In Spathegaster, the alternate
generation, the ovipositor is totally different, being small
and slender; and since it occupies little room within
the body we naturally find the abdomen altered in form.
This difference in the form of the ovipositor is a constant
one, even when the two generations are otherwise much

Spathegaster tricolor. 27

alike. Thus for example Nettroterus fumipennis and
Spathegaster tricolor resemble each other so much in
size and colouring, that from a superficial examination
they might easily be confounded ; but if we take into
consideration their whole structure, the form of the
abdomen, the length and shape of the wings, and
lastly the ovipositor, the difference between the two
generations is found to be sharply defined.

I will return hereafter to the consideration of the
interesting variations in the ovipositor, on account of
the importance of that organ. The principal forms
exhibited in the illustrations (Plate III) are ac-
curately drawn from photographs, so that the various
details will be found given in their proper relative
proportion.

As the two generations, just described as species of
Neuroterus and Spathegaster, belong to the same insect,
I felt strongly inclined to drop the usual practice of
designating them as of two genera ; but I have retained
these names, for the present at least, in order to avoid
confusion.

In the earlier descriptions of these two genera the
number of joints in the palpi were used as distinctions
between Neuroterus and Spathegaster. In Neuroterus
the maxillary palpi were said to be four-jointed and
the labial palpi two-jointed : and in Spathegaster they
were said to be respectively five and three-jointed.
But a closer examination of these forms has convinced
me that the maxillary palpi have invariably four, and
the labial palpi always two joints.

28 Observations on Cynipidae.

II. Aphilotrix Group.

The genus Aphilotrix includes a large number of
gall-flies among which I have been able to establish
a similar alternation of generations. Like Neuro-
tcrus the genus Aphilotrix is found only in the female
sex.

5. Aphilotrix radicis. Fbr.^

Gall. The gall is many-chambered, occurs on the
roots and lower part of the trunk, and varies in size
from a cherry to a man's fist. At first the gall is pale,
almost pure white when formed underground and
excluded from the light, and in consistence it resembles
a potato. Later it becomes brown and woody until it
is perfectly hard especially at its base. When it
reaches maturity the upper surface has a fissured and
uneven appearance and is of a brownish or black
colour. On section it shows innumerable round larva
chambers. (Fig. 5.)

Rearing the Fly, The mature galls which are found
in the autumn are collected and kept through the
winter in a cool place. The flies are perfectly developed
in autumn, as may be proved by opening some of the
cells, but they winter in the gall and do not emerge
until the following spring, about the end of April or
beginning of May.

Fly. Size, 5-6 mm. ; reddish brown ; the mesonotum
is marked by three darker longitudinal stripes, one
median and two lateral, and there is also a transverse

[' Cynips radicis, Fbr. Andncus radicis, Mayr.]

Aphilotrix radicis. 29

line in front of the scutellum ; further the metathorax,
and an irregular blotch on the first segment of the
abdomen, are also dark, as well as the bases of the coxae
and tibiae of the hind legs, and the claws. The thorax
is closely covered with silky pubescence : the antennae
are variously coloured, but the basal four joints are
reddish brown, and the apex dark.

Experimental breeding. After the flies quit the
galls they usually rest a few days before beginning to
lay their eggs. When I first made experiments with
this species in 1875 I expected them to select the roots
or the lower part of the trunk to lay their eggs in, but
I soon discovered that they always creep up the trunk
in search of the buds. After they have carefully
examined the buds with their antennae they begin to
prick them. They do this just as it is done by
a Neiiroterus, but the fly takes up its position nearer
to the base of the bud. It drives its terebra under
one of the bud scales until it reaches the foot of the
bud-axis. Thence it directs the channel not towards
the centre of the bud, in which lie the rudimentary
leaves, but below this point, and the tip of the terebra
thus enters tissues from which later shoots are de-
veloped. Some eggs may, it is true, come to lie upon
the base of the rudimentary leaves, but the greater part
will be found lower down, and there are usually no
galls found on the leaves themselves.

When the buds that have been pricked begin to
shoot, a long interval takes place before there is any
sign of gall formation. The earliest symptoms recog-
nizable are a delay in the development of the bud,

3© Observations on Cynipidae.

and the presence of more or less deformity and swell-
ing. A section through the parts exhibits little larva
cells lying in the swelling. From my first experiments
in breeding in 1875 I obtained undeniable evidence
that those galls which had hitherto been described as
belonging to Andricus noduli were produced by
Aphilotrix radicts. In the following year I repeated
the same experiment with the like success ; indeed this
species commends itself to the experimentalist, for
with it failure hardly ever occurs.

As 3. v\x\q Ajidricus noduli galls lie within the shoot,
but occasionally they are found in the petiole, because,
as I have already observed, the eggs of Aphilotrix radicis
sometimes come to lie within the range of the rudi-
mentary leaves. It is worthy of remark that occasion-
ally specimens of Aphilotrix radicis appear very late,
at the end of May or the beginning of June. By this
time the buds have expanded before they are pricked
by the flies, consequently a large quantity of eggs are
laid in the same shoot, giving it the appearance after-
wards of being perfectly covered with little nodidi galls.
From such a distorted shoot, scarcely an inch long,
sometimes as many as 200 flies will emerge. It is
hardly possible that so large a number of eggs could
have been laid in an unexpanded bud.

[The trufiBe gall occurs in September on Quercus sessiliflora,
Q. pedunculata and Q. pubesccns.

Inquiline. Synergus incrassatus which forms larva chambers around
the gall maker.

Parasites. Torymiis nobilis, T. erticanim, T. amoenns, T. radicis,
Ptcromalus querciuus, Tciras/ic/ius qucrcHs, Etoytoma rosae.']

Andriciis noduli. 31

5'^. Andricus noduli. Htg.^

Gall. The gall is scarcely 2 mm. long, and lies
within an oak-shoot of that year's growth, but is often
only recognizable from without by small round eleva-
tions of the bark. The mature galls form hollow
cavities in the substance of the wood, lined with thin
membranes. They are not unfrequently found in the
leaf stalks, which then appear thickened and swollen.
They give rise to more or less deformity (see Fig. 5 ^).

Bearing the Ply. To obtain the flies with certainty
the shoots on which the galls are formed should not
be collected too long before the flight time, otherwise
the wood is apt to become too dry. The time when
the flies emerge is variously stated, but I have con-
vinced myself by many experiments that they begin
early in August and go on to the middle of that
month.

It may, however, happen that a few flies do not
appear until the next year, these may come from late
individuals of Aphilotrix radicis, but in any case they
are a small minority.

Fly. Size, 2 mm. ; males and females differ in
colouring.

Female. Thorax black, dull, sometimes streaked
with orange; abdomen orange with a black blotch
on the back of the first segment ; the tip of the ab-
domen and ventral sheaths black. Legs testaceous,
the hind coxae dark ; antennae dark, at the base
testaceous.

[' Andricus irilineatus, Htg. .<4«rf/Va<s rflrfos, sexual form, Cameron.]

32 Observations 07t Cynipidae.

Male. Thorax and abdomen black, the latter
particularly shining ; legs light, dirty yellow, the coxae
and hind tibiae somewhat darker ; antennae dark, pale
at the base.

Experimental breeding. After a sufficient number
of specimens have emerged from the galls, a certain
interval must be allowed to elapse to make sure that
the females are fecundated. When satisfied by the
examination of the reccptacuhmi seniinis of several
females that they have been fertilized, the experi-
mental breeding may proceed. On account of the
small size of the fly, it is better to continue the
experiments on the same tree on which the galls
grew. Care must be taken, however, to see that the
flies can reach the roots easily. In order to secure
this I planted several oak saplings in pots, with the
long woody root turned up again towards the surface,
so that the extremity protruded from the earth near
the trunk. Even if the extreme point were to die off,
lateral rootlets would form so near the surface that
the flies could easily reach them. On an oak arranged
in this manner I made an experiment on August i8,
1878. I was soon able to satisfy myself that several
-Xii the flies, after exploring the surface of the rootlets
with their antennae, had finally pierced the root cortex
with their ovipositor. A subsequent examination of
the pricked spots revealed several eggs lying in the
cambium layer.

The number of eggs laid at one spot varies greatly as
shown by the size and number of larva cells in the
later Aphilotrix radicis galls. I believe it frequently

Andricus noditli. 33

happens that two or more flies lay their eggs close to
each other at the same spot. I cannot conceive how
otherwise the colossal compound galls sometimes found
could be formed. On one occasion I collected 1,100
flies from one Aphilotrix radicis gall ; as, however,
a single Andricus nodiili fly only carries about 500 eggs
in its ovarium, it is clear that such a gall could only
be produced by the co-operation of several flies.

On the little oak tree pricked in August, 1878, I was
able to watch the subsequent development of the galls.
In September a thickening of one of the pricked spots
gradually took place, the bark was raised and at last
broken through, and a new structure, of a hemispherical
form, was obtruded. When, in October, vegetation
ceased and the leaves began to fall, the growth of the
gall stopped, but only to resume its course next spring.
In this first stage of its growth the gall had the con-
sistence of a potato, and sections could easily be made
for the purpose of microscopical examination. The
apparently homogeneous tissue was found to be studded
with countless minute larva chambers. In the centre
of each of these chambers lay a very small larva
surrounded by a succession of concentrically arranged
cells. The cells next the larva were the largest, were
filled with starch granules, and some were undergoing
degeneration. The cells of the more remote layers
became steadily smaller until they finally passed into
the surrounding cambium tissue. Here and there
vascular bundles pushed their way into the newly
formed stroma, and brought it thus into closer con-
nexion with the parent tissue from which it grew.

D

34 Observations on Cynipidae.

About May the larva was fully developed, and the
gall, which had finished its growth, had become woody.

In the course of the summer each larva passes into
the pupa state ; in the autumn the perfect flies are
found, but they pass the winter within the galls, and
only emerge in April of the next year.

It is remarkable that two years are required for the
completion of this generation cycle. A certain pro-
portion of the Aphilotrix radicis generation emerges in
April of the first year, and the remainder in April of the
second year ; in the interval we have the sexual
generation and the prolonged larval stage oi Aphilotrix
radicis itself

[The knot gall is found in June on Q. pcdimadaia, Q. sessili/lora,
and Q. pubescens.

Inquilines. Ceroptres araior in May and June of the second year:
Sapholytus connatus, Synergus apicalis in May and June of second
year : S. vulgaris.

Parasites. Megasiigmus dorsalis and Pteromalus quercinus. This
gall is often found on Lammas shoots.]

6. Aphilotrix Sieboldi. Htg.^

Gall. The galls are usually thickly aggregated on
slender oak twigs, or on young trees, most frequently
close to the ground. They are conical, and when fresh
are covered with a beautiful cherry-red rind. They are
found thus in June, but in the autumn when the galls
are mature, the sappy outer rind dries, withers and
drops off. Then the woody inner gall appears, like
a firm cone, with regularly formed ridges running from

\} Cynips Sieboldi, Htg. C. coriicalis, Schenck. Andriats Sieboldi,
Mayr.]

Aphilotrix Sieholdi. 'i^

the apex of the gall to its base. The tissue of the
gall penetrates deeply into the wood of the oak and
the smaller stems often die in consequence of this
encroachment. (Fig. 6.)

Rearing the flies. The fly is very easy to rear if the
mature galls are collected in the autumn and kept
through the winter in a cool place. Next spring, at
the end of April or beginning of May, the flies begin to
leave the galls.

Fly. Size 4-5 mm. almost uniformly reddish brown ;
the front of the thorax is marked by some fine black
lines, the metathorax is somewhat darker. Legs
uniformly reddish brown. The whole thorax very
hairy. Antennae dark, pale at the base. The fly is
very like Aphilotrix radicis but rather lighter in colour.

Experimental breeding. It is not difficult to watch
the fly while ovipositing. It behaves like Aphilotrix
radicis, and the buds are similarly pricked, the fly
pushing its ovipositor into the base of the bud-axis.
The eggs, however, are usually placed in the area of
the rudimentary leaves, and galls extremely like those
of Andricus nodtdi are formed in the stalks and veins
of the leaf These have hitherto been described as
Andricus testaceipcs. To make sure, and to avoid con-
fusion with the Andricus noduli gaWs, I have for several
years made experiments in breeding, invariably keeping
the little oak trees under strict control in a room ;
but I have always obtained the same galls, resembling
the galls of Andricus noduli.

[The red barnacle gall is biennial, living about fourteen months, and
is found on Quercus sessiUflora and Q. pedunculata.

D 2

36 Observations on Cynipidae.

Inquiline. Synergus incrassatus.

Parasites. Torymus nobilis, Euryionia rosae and Olinx trilineata.
These galls are attacked frequently by Tits and have the larvae
picked out.]

6=^. Andricus testaceipes. Htg.^

Gall. In many cases the galls are only recognizable
by a round or tumid thickening of the stalks and veins
of the leaf (See illustration, Fig. 6^.) Within this
thickening lies the gall, a hollow chamber scarcely
2 mm. long, separated by a thin membrane from the
surrounding tissue : but this gall also occurs inside the
wood of the shoot, and it is then impossible to distinguish
it from the gall oi Andricus noduli. The flies emerge,
like Andricus noduli, at the beginning of August.

riy. Size about 2 mm. Female, thorax black and
dull, abdomen orange, back of the abdomen and ventral
sheath dark, legs orange. Male. Entirely black, abdo-
men shining, legs pale yellow. This species cannot be
distinguished with certainty from Andricus noduli.

Experimental breeding. If the number of flies be
sufficiently large it is not difficult to observe them
ovipositing. The fecundated females betake themselves
for this purpose to the slender shoots or stems, and
pierce the bark close to the ground. As a rule the eggs
are laid in a ring within the bark of the selected shoot.
Gall formation begins in the course of September.
The bark at the pricked spots becomes thickened, and
soon rises above that of the uninjured parts. If thin
tranverse sections are made through the thickened
portions, spherical masses of cells are seen in the
[' Andricus Sieboldi, sexual form, Cameron.]

Aphilotrix corticis. 37

cambium layer, with a central chamber in which the
larva lies. At the beginning of the cold weather gall
formation is arrested, to be resumed and rapidly com-
pleted in the following spring. In May the thickening
of the bark increases very much, distinct roundish
swellings are formed, which burst and disclose the
beautiful red conical galls. They grow 4-5 mm. above
the level of the bark, and their bases are rooted in the
substance of the wood. In June they reach maturity,
and in autumn the fly is fully formed, but passes the
winter in the gall '.

[The leaf-vein gall is found in June on Q. sessiliflora.
Inquilines. Synergits apicalis and Ceroptres arator.
Parasite. Megastigmus dorsalis.']

7. Aphilotrix corticis. L.^
Gall. These galls are found in the bark of thick oak
roots, or in the swellings that form around old injuries
to the bark, like those usually seen where boughs have
been sawn off. When fresh the gall appears of a hemi-
spherical or oval form, covered by a sappy, reddish
yellow, or ochrey envelope. The real larva chamber
lies under the level of the bark and penetrates by
conical points into the substance of the wood. The
bell-shaped upper half dries after maturity and falls

* These, like other galls, are greatly exposed to the attacks of
various parasites (species of Torymus and Synergus\ and it is in-
teresting to observe how the gall has indirectly evolved a means of
protection. The red sappy envelope secretes a sticky fluid which is
eagerly sought after by ants, and that they may enjoy this nectar
undisturbed, they build with sand and earth a perfect dome over the
galls, and in this way provide the inhabitants with the best possible
protection against their enemies.

['■^ Cynips corticis, Hartig. Atidricus coiiicis, Mayr.]

38 Observations 07t Cynipidae.

off, presenting then quite a different appearance, and
disclosing the base of the gall sunk in the bark. It is
surrounded by a sharp somewhat raised rim which
bears on its inner side a row of uniformly pierced
punctures. These little openings belong to an earlier
period of growth; and through them passed the
vascular bundles that nourished the upper sappy half
of the gall. Subsequently the fly gnaws the hole by
which it emerges in the centre of the base. (Fig. 7.)
The method of rearing and time of appearance are
the same as in the other species oi Aphilotrix.

Fly. Size 4 mm., the whole insect dark, of a brownish
black colour. Margins of the orbits, base of the
antennae, ventral keel and legs bright reddish brown ;
apex of femora paler as a rule. Thorax dull, covered
with silky hairs.

Experimental breeding. These flies are easy to
rear. Soon after they leave the galls they begin to
prick the buds, giving a preference to those buds
which have already begun to shoot. They push the
ovipositor so deeply into the bud that the eggs are
deposited on the base of the leaf germs. It might
naturally be supposed that from their great resemblance
to the two previous species a similar gall would be
formed, and at first I expected to find a gall like
Aphilotrix Sicboldi, but the experiments which I made
in 1877-1879 satisfactorily cleared the matter up.
Between May 6 and 8, 1877, twenty buds on a little
oak tree placed in a room were pricked by Aphilotrix
corticis. When in June the oak was in full leaf,
I noticed here and there on a leaf-stalk, or in the axil

Andricus gemmatus. 39

of a leaf, little greenish or brown elevations about
I mm. high. As it happened I obtained no flies, for
I had overlooked the time when they emerge and had
allowed it to pass ; all I could vouch for was, that by
the beginning of August the flies had left the galls.
In 1878 I repeated the experiment; between April
23 and 28, ten buds were pricked ; and between May
3 and 6, twelve buds on a second oak. In June the
same little galls appeared, from which the flies emerged
at the end of July. In 1879 I made the experiment
for the third time with similar results.

[The bark gall is found in September on Quercus sessiliflora,
Q. pcdiincidata and O. pubescens.
Inquiline. Synergus inaassatus .
Parasite. Torynius cofiicts.^

7^. Andricus gemmatus. n. sp.^
Gall, These galls are small and inconspicuous,
scarcely 2 mm. long, and they are often overlooked
because their apices are frequently the only parts that
project. They are usually formed in the axil of a leaf,
near the later winter buds, and apparently spring
from the rudimentary bud. They are also sometimes
found free on the shoots. It is possible that the egg
is sometimes laid exactly in the axil of the later leaves,
and this may give the gall the appearance of growing
out of a little axillary bud. The gall consists of
a thin smooth rind which at first is green but later of
a brownish colour ; and it can be recognized most
easily by the hole through which the fly has emerged.
(Fig. ']^.) Neither gall nor fly has been hitherto
[^ Andricus cotiia's, sexual form, Cameron.]

40 Observations on Cynipidae.

described. I have chosen the name from gcmmare, to
bud, because the galls at first resemble little buds.

Fly. Size 2 mm. long. Female, black ; thorax dull,
sparsely haired ; abdomen very shining, the ventral keel
reddish brown ; legs orange, coxae and posterior tibiae
dark ; antennae orange at base, apex dark. Male^
black ; abdomen very shining ; legs somewhat paler,
coxae and femora dark ; base of antennae pale. They
emerge at the end of July and beginning of August.

I have been unsuccessful in carrying out experi-
mental breeding with this generation of Andriciis, on
account of the small number of flies I have been able
to collect, and I could not therefore follow directly the
formation of the Aphilotrix corticis gall. Besides, it is
very difficult to get suitable oaks for such experiments,
because these flies lay their eggs exclusively in tumid
thickenings of the bark.

[The bud gall is found on Q. sessiliflora in May and June.]

8. Aphilotrix globuli. Htg.^
Gall. This beautiful green globular gall does not
burst from the bud until September, and its base is then
closely surrounded by bud-scales. When fresh the
gall is covered by a sappy green rind, underneath
which is the woody inner gall, with a large larva
chamber. In October the gall falls out of the bud, the
sappy rind is loosened and the woody inner gall left
bare. But if the galls be collected when fresh, the
green rind dries on, and shows an uneven reticulated
surface, according with the description which we often
n Cynips globuli, Htg. Andnats globuli, Mayr.]

Aphilotrix Globtili. 41

find given of this gall. The woody inner gall is marked
by regular furrows and ridges. (Fig. 8.)

Rearing the fly. There is some difficulty in rearing
this fly because of the long duration of the larval state.
Although the larva is full grown by the end of October
it does not enter the pupa state that year. The state-
ment that the flies appear in the following spring is
founded on error. The larva state continues into the
next year, and it pupates in the autumn, and the
fly appears in the April following. But if the galls,
when collected, are not kept as much as possible in
the same condition as if in the open air, it is very
difficult to rear the flies. The galls must therefore
pass the winter in the open air in the way previously
described, and it is only by this means that the larva
can be got to undergo its metamorphosis successfully.
If the galls are kept in a room the metamorphosis does
not take place. I have kept galls with fully developed
larvae for several years without obtaining a single fly.
From the galls which pass the winter in the open air
the flies as a rule emerge in the second, but in some
cases not until the third year. Thus from the galls
which I collected in October 1876, I obtained the flies
in April 1878, but some did not emerge until April 1879.
The same peculiarity occurs with several other species
which I shall describe later.

Fly. Size 4 mm. long, head and thorax black, dull,
thickly haired ; abdomen very shining, dark above,
reddish brown below ; antennae dark throughout ;
femora reddish brown, but the coxae and tibiae of the
middle and hind legs infuscated.

42 ObservaHotts on Cynipidae.

Experimental breeding. The flies emerge very
early, some even by the end of March. On March
30, 1878, I made the following observations. Five
pricked buds were carefully marked by threads tied
round them. When pricking the flies behaved in
a similar way to the species of Aphilotrix previously
described. The ovipositor was again directed under
the bud-scales and pushed on towards the base of the
bud, so as to place the eggs not in the germs of the
leaves but below them, and tolerably accurately in
the centre of the bud-axis. Only one egg was laid in
each bud, and each separate act required about twenty
minutes. I naturally expected from this that out of
each pricked bud only one gall would develop. The
five pricked buds began to shoot in May ; one, however,
lagged in growth, and showed obvious signs of
thickening. It soon became apparent that this was
due to gall formation, and it afterwards developed the
gall described as Andriciis inflator. I only obtained
one gall from this experiment. In the following year
I repeated the attempt. On March 25, 1879, several
flies were put upon a little oak and among them they
pricked nine buds. In May I obtained two galls of
Andricus mflator.

[The globular gall is found in September on Quercus sessili/lota and
Q. pubescens.

Inquilines. Neurotcriis parasiticus, Synergus riificotitis in July of
second year, S. ncrvosHS and S. vulgaris.

Parasites. Torymits regius ; Siphonura chalybea ; Megastigmus
dorsalis, Euryioma rosae, Eiipebnus azureus (probably hyper-para-
sitic).]

Andricus injlator. 43

8^. Andricus inflator. Htg.^
Gall. This gall is developed from a bud, is of
a green colour, and has a foliaceous covering. In
appearance it resembles an enormously thickened and
shortened shoot. In the first year growth is not per-
ceptibly interfered with, and the winter buds are formed
in the ordinary manner above the gall in the axils of
the leaves. Next year, however, all these shoots die
away. A longitudinal section exhibits a cylindrical
cavity within the gall, at the lower end of which there
is a little inner gall-chamber from which the fly proceeds.
The upper end of the cavity is closed by a covering
which is at first red and later of a yellowish colour.

(Fig. 8^)

To collect the flies the galls must be gathered in the
middle of June. The flies emerge at the end of June
or beginning of July.

My. Size 2-4 mm. Head and thorax black, slightly
shining ; abdomen in the female black above, red or
orange beneath ; in the male, entirely black ; legs
orange, but the posterior tibiae and coxae dark ;
antennae dark, pale at the base.

Experimental breeding. The females as soon as
they emerge and have been fecundated seek out the
most tender buds, either terminal or axillary, and lay
one egg in each bud. Sometimes the flies also prick
those axillary buds which have been formed on the gall,
and from these pricked buds the Aphilotrix globuli galls
develop in September. In this way the singular fact

[' Andricus globuli, sexual form, Cameron. Cynips injlator, Thorns.]

44 Observations on Cynipidae.

is easily explained that an Andricus injlator gall is
often found super-imposed on one or more Aphilotrix
globuli galls. I have only made observations on
Andricus injlator in the open air, and have not been
able to make any more exact attempts at breeding.

[The twig gall is found in May on Quercus pcduncidata and
Q. pubescens.

Inquiline. Sapholytiis conttatus.

Parasites. Alcgasttgnms dorsalis, Torymus auratus, Decatoma
Necsi, Pteronialns dissectus and P. Erichsoni. The gall often exhibits
buds upon it in the following year, and is perennial as regards its
growth. The fly has the mesonotum uniformly shagreened, twelfth
and thirteenth joints of antennae longer than broad, mesopleura
striated.]

9. Aphilotrix collaris. Htg.^
Gall. These galls are easily overlooked from their
small size. They are formed upon a bud, and when
ripe are so deeply concealed within the bud-scales that
only the apex of the gall can be perceived. They are
conical, of a reddish brown colour when fresh, and
from the base of each there springs a slender appendage
which penetrates deeply into the axis of the bud. In
September or October the gall becomes loosened and
falls to the ground, and the appendage shrivels up and
falls off, but very often we find galls remaining in the
buds which on further examination prove to be adherent
to them ; hence the assertion that this gall passes
the winter in the bud. But it has been proved that
only inquilines or parasites are reared from those
adherent galls : we have an instance in this of wh^t
is frequently found to be the case, that when an inquiline
[' Cynips collaris, Htg. Andricus collaris, Mayr.]

Aphilotrix collaris. 45

lays its &%^ in an immature gall, the growth of the gall
is altered with the death of the original larva, and
becomes pathological. Sometimes these morbid galls
remain small, at others they become jfirmly rooted into
the parent tissue. (Fig. 9.)

Rearing the fly. The same precautionary measures
must be taken as in the former species of Aphilotrix
in order to obtain the flies from the galls. The duration
of the larval state is the same. After the galls are
mature, a year and a half passes before the appearance
of the flies.

Fly. 3 mm. long. Head and thorax dark, often with
reddish lines on the back ; thorax smooth and shining ;
scutellum reddish brown, dull, and hairy ; abdomen dark,
base sometimes reddish ; legs orange ; coxae always
dark, and sometimes also the bases of the femora.

Experimental breeding. This fly has hitherto passed
as rare, chiefly because the galls are difficult to find, and
the rearing does not always succeed. Further observa-
tion has shown me, however, that in some years it is
very common. I made my first attempts at breeding in
1876 with two flies, which pricked several buds between
April 4 and April 6. The eggs were always laid in
the rudimentary leaves in the centre of the bud, and
accordingly it proved, as might have been expected,
that the galls developed on the leaves. As soon as the
buds had unfolded, a tumid thickening was observed on
two of the leaves. This was the beginning of a gall
which was soon recognizable as Andricus curvator.
I repeated the experiment in 1878, putting six flies
on a little oak, the buds of which they continued to

4*5 Observations on Cynipidae.

prick for several days. The result was convincing, as
in June the little oak was perfectly covered with the
galls of Andricus curvator. The illustration was taken
from a shoot of this oak.

[The collared bud gall is found in August or September on Quercus
sessiliflora.

Inquilines. Synergus nervosus and S. palliceps.

Parasites. Eurytoma verticillata and Syntomaspis caudatits.']

9*. Andricus curvator. Htg.^
Gall. The gall forms on the leaves, and appears in
May as an irregular thickening of the leaf surface. At
first it presents, when cut through, a solid kernel, but
as time goes on a cavity is gradually formed, and from
its inner wall projects a small brown central gall. If
several galls are formed on the same shoot, the
leaves are hindered in their development, and remain
rudimentary. The flies emerge in June.

Ply. Size 1-5 to 2 mm. Black. Thorax smooth,
sometimes rather rugulose, without sculpture ; abdomen
black and shining ; legs testaceous ; coxae always, and
femora often, dark. Males and females similar.

Experimental breeding. I have made many experi-
ments with this species. If the fecundated females are
placed on an oak sapling, as a rule they soon begin to
prick the buds. To do this the fly perches on the point
of the bud, and bores its ovipositor obliquely downwards
into the interior. Only one egg is laid in each bud, and
a long time elapses before any gall formation can be
seen. The gall begins to develop in September, but
occasionally as early as August. At first the gall is
[^ Cynips atrvator, Thorns. Andricus per/oliatus, Schenck.}

Aphilotrix fecundatrix. 47

difficult to recognize, as its brown point scarcely shows
beyond the scales of the bud, but when mature it projects
more distinctly, and its base is gradually loosened from
the tissues of the bud-axis. Before it was known that
Aphilotrix collaris and Andriciis curvator were alternating
generations, it was supposed that the egg laid by
Andricus curvator in June rested in the bud until the
next year, and that then, when the period of growth
returned, Andricus curvator galls were formed once
more on the leaves. This was all the more easy to
believe, because the bud in which the egg was laid in
June, rests until the next year as a winter bud, and
does not naturally develop in the same year. We see,
however, in this, as in other cases, that a dormant bud
may be induced to shoot by the larva.

[The curved leaf gall is found in June, and sometimes on Lammas
shoots, on Quo'cus pedunculata, Q. sessiliflora and Q. pubescens.

Inquilines. Synergus alhipes, S. apicalis, S. facialis, S. radiatiis
and S. ihatimacera in June of the same year; and Peridistiis Brandti.

Parasites. Torymns auratus, T. abdotniitalis, Pteromahts cordairii.
P. tibialis, P. ttieconatus, P. Saxesenii, P. dissecUts, P. Erichsoni
P.jucundiis, in June and July of the first year; Eurytoma gracilis, in
August ; Entedon sciancitrus, E. cecidomycanms, EulopJms laevissinius,
E. ntetallicus, Siphonura viridiaenea, Mesopolobtts fasciiventris, Tele-
nomus phalaenanim, Dccatonia biguttata, D. Neesi, Eurytoma rosae,
Syntomaspis dubitts, Pletirotropis metalliciis, Elachestiis petrolatus, and
Eupelntus annulatus. The larva chambers of the Synergi are usually
near the surface and do not interfere with the gall-maker.]

10. Aphilotrix fecundatrix. Htg.^
Gall. This gall, which resembles a hop, is surrounded
by closely imbricated scales, at first of a green colour,

\} Cynips gemmae, Lin. Cynips fecundatrix, Htg. Aphilotrix
gemmae, Mayr, Fitch, Andricus fecundatrix, Mayr.]

4^ Observations on Cynipidae.

but brown later ; these then loosen and fall off. At
the base of the cone there is a small inner gall of an
elongated oval form, which at maturity becomes detached
and falls to the ground. At first this inner gall is firmly
adherent to the bud-axis, but in August this adhesion
gives way owing to the contraction of the base, by which
the scales are compressed more tightly together until
they finally thrust the inner gall completely out. In
this state the gall is of a yellowish green colour, and
still of a soft consistence. The period of full maturity
is reached on the ground, when the whole gall becomes
dark, very firm, and hard, affording the larva ample
protection against the influence of the weather. It is
to be noted that galls sometimes remain concealed
among the scales of the outer gall. (Fig. lo.) In
many cases in a well developed outer gall, the inner
gall may turn out to be small, round and rudimentary.
These galls are found to contain one or more inquiline
larvae, lying in separate loculi, and it is through their
influence that normal development has been stopped
and perverted.

Rearing the My. Although the gall is very common
it is difficult to rear the fly successfully, for the larval
state is very prolonged, and it is not easy to maintain
the natural conditions of life during that period. The
wintering must take place in the open air. The larva
lies dormant as long as tha.t of Aphilotrix co//an's ; I only
obtained the flies in April 1878 from the galls collected
in August 1876, and the flies of some galls did not
emerge until the third year. If the galls after being
collected are kept in a room, the metamorphosis of the

Aphilotrix fecundatrix. 49

larva does not proceed ; it may remain alive in the galls
for several years, but at length it dies. In what way
the alteration of the environment acts it is difficult to
tell, but the operation of such atmospheric influences
as cold, damp and heat appears to be absolutel}^
necessary to secure the regular progress of meta-
morphosis. The flies emerge in April.

Fly. Size 4-5 mm. The whole fly dark, almost
black ; thorax dull, rugose, with white silky hairs ;
abdomen black and shining, but the sides more or
less reddish brown ; legs dark as a rule, the knees
distinctly reddish brown, front legs at the widest part
sometimes bright reddish brown, the upper part of the
femur dark.

Experimental breeding. In conducting experiments
with this species I have had some difficulty because the
fly only lays its eggs in male catkin buds. As the
little oak trees which I planted in pots produced no
flowers, there was nothing to be done but to watch the
flies ovipositing in the open air. I succeeded, on
April 14, 1878, in accurately observing several of them
while in this act, but to be quite clear about their
manner of ovipositing, I allowed some flies reared by
myself to pierce branches which I had cut off and
brought indoors for the purpose. I found that the fly
directed its ovipositor under the bud-scales until it
pierced an anther, when it laid the egg in it. It was
therefore certain that the gall would be formed on the
anther. During my observations made in the open air,
several buds were pierced under my own eyes, and
I marked these by tying a thread around them. When

E

5© Observations on Cynipidae.

the male flowers developed in May following, delicate
little galls could be seen on these pricked buds, situated
either singly, or several together, on the pedicels of the
flower, I found the same galls on two different trees,
both of which had been pricked hy A philotrixfecundatrix.
I therefore felt satisfied that no mistake or deception
was possible. The galls, about to be described, were
evidently those of a species of Andricus. It is to
be observed that the Aphilotrix fecundatrix pricks by
preference, and perhaps exclusively, the flower buds of
Quercus robur {pedunculata, Ehrh.). The reason for
its preferring this species of oak is probably because
it flowers about fourteen days earlier than Quercus
sessiliflora.

[The artichoke or hop gall is found in July on Quercus sessiliflora,
Q. pedunculata, and Q. fubescens.

Inquilines. Synergus melanopus, S. evanesceiis, S. apicalis, S. vul-
garis, A ulax fecundatrix.

Parasites. Eurytoma signata, Syniontaspis caudaius, Torymus
regius {Callimome incottstans), Megastigmus dorsalis, Mesopolobus
fasciiventris , Olinx trilincata, and Entedon leptoneurus. The moth
Carpocapsa Juliana in the outer gall.]

10^. Andricus pilosus. n. sp.^
So far as I know this gall has not hitherto been
described. I have selected the specific name ' pilosus '
because it is covered with short hairs and these serve
to distinguish it from similar species.

This elegant little gall is about 2 mm. in length, of an
elongated oval form, with a prominent apex, thin-walled,
green at first but when mature of a brownish colour,
covered with pale stiff" hairs. The galls are found

[^ Andricus fecundatrix, sexual form, Cameron.]

Andricus pilosus. 51

among the anthers on the catkins either singly or
several together. (Fig. iO'\) In order to rear the flies,
the galls should be gathered in the end of May shortly
before they are mature, and the flies are then obtained
about the beginning or middle of June.

Ply. 1-5 mm. long; black; thorax smooth, slightly
shining, scutellum rugose ; abdomen uniformly black,
shining; legs from the coxae to the lower third of the
femora uniformly dark, the remainder yellowish-testa-
ceous ; antennae yellowish, the apices fuscous. The
male has the same colouring but the antennae are almost
wholly dark.

Experimental breeding. I made a series of experi-
ments with this species in June, 1878, both indoors and
out. In some cases I brought the fly straight to the
oak sapling, and in others I tied the gall upon the
sapling shortly before the escape of the fly. The
flies seek by preference the tenderest axillary buds
which they begin to prick. When they have selected
a suitable bud they poise themselves on its summit and
bore the ovipositor obliquely from the surface into the
centre of the bud. They lay only one egg in each bud,
and this invariably occupies from twenty to thirty
minutes. While ovipositing the flies are so indifferent
to interruption, that it is possible to cut off the twig
which they are piercing, and place it under the micro-
scope for better observation. As soon as one egg is
laid they immediately seek out a new bud. The average
duration of life in this species is about eight days.

In my experiments in June, 1878, I marked in all
twenty-six buds as having been pricked, sixteen indoors

£ 2

q2 Observations on Cynipidae.

and ten out. By the beginning of July, it was possible
to perceive a change in some of these buds, for they were
noticeably thicker and larger; and by July lo, I was
able distinctly to recognize that it was the Aphilotrix
fecundatrix gall that was forming. The little oak trees
pierced indoors produced three, and those out of doors
four galls. It was in this case again remarkable how
few of the pricked buds produced galls.

[TJie hairy catkin gall is found in May on Oiiercus sessiliJlora?\

11. Aphilotrix callidoma. Htg.^
Gall. These, which are the most elegant of our
North German galls, possess a certain historical
interest, for they were described by Malpighi ^ in
1682. In spite of this it has only been in quite recent
times that its fly has been successfully reared. So far
as I know, Giraud ^, in 1859, was the first to breed and
describe the fly.

The gall, which springs by a slender stalk of varying
length from the axil of a leaf, is spindle-shaped or
fusiform, and is marked by regular, sharply defined,
longitudinal ribs. It is usually green with ribs of a red
colour. (Fig. II.)

The galls appear at different times, sometimes in
July, and sometimes in August. They mature quickly,
and the earliest fall to the ground at the end of July.
To rear the flies, the mature galls should be collected

[^ Cynips callidoma. Thorns. Andricus cirratus, agamous form,
Cameron. Andricus callidoma, Mayr.]

^ Malpighi, Plant, aiiatoni. II. De gallis.

^ Signalements, &c. de Cynipides, Verhdl. zool.-bot. Ges. Wien, ix.
PP- 337-74.

Aphilotrix callidoma. $'}^

and left on damp sand until they begin to get brown,
which is a sign that the larva is full grown ; they should
then be kept in a cool place or in the open air through
the winter. Some of the flies appear during the next
spring, but others lie dormant until the second year.
It is probable that galls maturing early hatch out in the
first year, and that those maturing late do so in the
second year. It is particularly to be remarked that the
majority of the galls are beset with parasites, and this is
probably the reason why the fly has not been identified
before.

Fly. 4 mm. long ; reddish yellow ; antennae, sutures
of the thorax, and margins of scutellum, black ; the back
of the abdomen dark brown ; head and thorax sparsely
haired ; legs yellowish brown, trochanters only black ;
posterior tibiae brown.

Experimental breeding. The flies emerge in April
and seek the male catkin buds in which to lay their
eggs. For this reason I have only been able to watch
them ovipositing in the open air, or on branches cut
off for the purpose. The fly la3^s its ^%^ upon and
between the anthers, while they are enclosed in the
bud ; and there are often a great many laid in the same
bud. In April, 1878, I marked a number of buds pricked
in the open air. At the time when most buds were more
or less developed those which had been pricked were
remarkably backward, only a few flowering catkins
projecting from them. On further examination it was
seen that the anthers were quite distorted by small
closely set galls. This gall, which I am about to
describe, was that oi Andricus cirratus.

54 Observations on Cynipidae.

[The stalked spindle gall is found in July and August on Qiiercus
sessiliflora.

Inquilines. Synergus nervosus and S. vulgaris.

Parasite. Siphonura brevicauda. Cameron considers Aphilotrix
callidoma the same as Aphilotrix quadrilineata and sa3's he can find
no distinguishing characters in the two flies. Cameron, Hymenoptera,
vol. iv. p. 97.]

11''. Andricus cirratus. n. sp.

This gall has not been described before. I have
chosen the title cirratus on account of the tuft of hair
{cirrus) which the gall bears on its apex.

Gall. Size about 2 mm. ;. oval with a rounded point ;
when fresh of a green, and when mature of a brownish
colour. The rounded end of the gall bears a tuft of
long thick whitish hairs three or four times the length
of the gall. The gall is placed on the stalk of the male
catkin ; at its base two shallow impressions may be
recognized which are derived from the sutures of the
anthers from which the gall sprang. The galls are
often placed so closely together that they appear to
form one woolly mass ; the separate catkins are then
more or less distorted and only a white tuft of hair can
be seen projecting from the open bud. (Fig. ii*".)
The fly is very easily reared if the galls are collected
at the end of May or the beginning of June.

Ply. Length 1-5 mm. ; black ; thorax dull ; scutellum
rough ; abdomen reddish yellow on the sides ; legs
uniformly citron yellow, the posterior trochanters dark ;
antennae testaceous with dark apices. The males
are similarly coloured, but the abdomen is somewhat
lighter.

Experimental breeding. When in the beginning of

Aphilotrix Malpighii. ^^

June, 1878, a great number of the flies had emerged,
I put them, on June 8, on an oak saphng and saw them
begin to prick the small axillary buds, of which fourteen
in all were marked. About four weeks afterwards, on
July 5, I observed galls developing on three buds, which,
as they grew out of the buds with long stalks, were soon
recognizable as Aphilotrix callidoma galls. In the
beginning of August two more galls developed ; the
cause of this delay is difficult to explain, as all the buds
were certainly pricked at the same time. The gall
grows very quickly, reaches maturity in three weeks,
and then falls to the ground.

[The tufted gall is found in May on Querciis sessiUflorai\

12. Aphilotrix Malpighii. n. sp.^
Gall. This gall is very like the preceding one and
of the same spindle shape, but shorter and more com-
pressed ; and it is usually either without a stem or with
a very short one. The time of maturity is different : it
appears much later than the former gall, does not show
itself out of the bud until September, and arrives at
maturity in October. (Fig. 12.)

The development of this fly differs from the preceding.
The gall which matures in October undoubtedly con-
tains the full grown larva, but this does not enter the
pupa state in the same year. It rests till the next year,

' On account of the great resemblance to the Aphilotrix callidoma
gall it has often been confounded with it, but the fact that it possesses
a totally different sexual generation marks it as a separate species.
In memory of the circumstance that Malpighi nearlj' 200 years ago
described the Aphilotrix callidoma gall, I have called the present
species after him. \Andricus Malpighii, Ma3'r.]

^6 Observations on Cynipidae.

enters the pupa state in the autumn, and the flies
emerge in April of the second year.

Fly. 3 mm. in length ; reddish yellow, darker than
Aphilotrix callidoma ; thorax with black streaks, upper
part smooth, sides sparsely haired, scutellum rough ;
back of the abdomen dark brown ; legs reddish yellow,
trochanters all brownish, as well as the upper half of
the femora and outer surface of the tibiae ; antennae
black. The colouring of this fly is so like that of
Aphilotrix caliidouta that it can only be distinguished
with certainty from it when it has been reared from the
gall. I have not been able to make experiments in
breeding with this fly, but I have made some experi-
ments with the corresponding sexual generation and
these have afforded me trustworthy results.

[Malpighi's gall is found in September on Quercns sessiliflora.']

12*. Andricus nudus. n. sp.^
Gall. This little inconspicuous gall, 1-5 mm. long, of
an elongated oval form, with distinctly depressed apex,
is found on the flower stalks of the male catkins between
the anthers. The gall is naked but at its point it has
a few little hairs. When fresh it is green but yellow
when mature. (Fig. i2«.)

To rear the flies the galls must be collected at the
end of May ; the flies emerge in June.

Experimental breeding. I succeeded in breeding
these flies without any difficulty. In 1877 I made my
first experiment. A quantity of fecundated females

' This species also has hitherto been undescribed. I have chosen
tlie name nudus because it differs from the ciyyatus in being perfectly
bald.

Aphilotrix autumnalis. ^'j

were placed upon an oak sapling, and on June ii ten
buds were pricked by them. These active little flies
always choose the most tender axillary buds. Care
must be taken therefore in experimental breeding to
select only those oaks which have buds of a soft and
tender consistence. 1 1 was long before any change could
be seen in the pricked buds, and it was not till
September 3 that two of them showed the beginning of
gall formation. On October 2 a third gall appeared,
and all three galls were those described above as
Aphilotrix Malpighii. In April, 1879, I got two flies out
of these three galls. I made in 1878 a second experi-
ment in breeding with Andricus niidus, and from the
collected galls I obtained the first flies on May 30. On
June I. I put them on a small oak. I observed that
several of them began at once to prick, and eighteen
buds were marked in all. In the beginning of Sep-
tember three galls grew out of these buds, and four
more at the end of the month ; consequently the con-
nexion between Aphilotrix Malpighii and Andricus
niidiis appeared to me sufficiently proved.

[The bald seed gall is found on Oitercus sessiliflora in May.

Fly. Length i-2 to 1-6 mm. black, abdomen paler, testaceous on
ventral surface, thorax slightly shining, legs uniformly yellow ;
antennae of same colour except the fourth and fifth joints which are
darker. Males have the femora and tibiae dark, as also the antennae,
except the second and third joints which are bright yellow, meso-
notum finely shagreened and shining.]

13. Aphilotrix autumnalis. Htg.^

Gall. This gall, like the Aphilotrix globuli galls,

[' Cynips autumnalis, Hartig. Andricus autumnalis, Mayr. An-
dtivus ramitli, agamous form, Cameron.]

58 Observations on Cynipidae.

described above, developes from a bud, and its base
is surrounded by the bud-scales. It is of an elongated
oval shape with a distinctly depressed umbilicus at the
apex, and when fresh it is covered with a brown sappy
rind. The gall is formed in October, and at the end of
the month, when mature, it falls out of the bud to the
ground. The sappy rind is then loosened from the
woody inner gall, which shows on its surface faintly
marked furrows. (Fig. 13.)

The fly does not appear until the second year. The
flies emerged in April, 1878, from the galls collected
in October, 1876.

Fly. Size 3 mm. long ; head and thorax black ; the
latter dull and wrinkled ; abdomen shining, dark on
the back, reddish brown on the sides ; legs reddish
brown, trochanters dark. Appears in April.

It was to be expected that an alternate generation of
this species would be found, not only from its great
resemblance to Aphilotrix globuH, but also from the
time of the gall's appearance. The flies emerge in
April, but, as the galls are not formed until October,
in a winter bud that is not in existence in April,
it is evident that another generation, which forms the
gall, must intervene. I have not made direct experi-
ments in breeding with Aphilotrix autumnalis, but I have
watched these flies ovipositing. At first I believed that
they would prick flower buds only, as it was these that
they pricked so vigorously under my own observation
when I put some flies on detached twigs. I convinced
myself afterwards that they pricked other buds without
making any distinction. Perhaps the flower buds may

Andricus ramuli. 59

receive a preference because they are larger and
develop earlier. This fly lays a multitude of eggs
in the same bud, and sometimes bores round the whole
periphery of the bud, so that later a large number of
eggs are found within, each separate, but all packed
closely together. The eggs are laid either on the leaves
or on the anthers. I have not reared flies from the
resulting gall myself, but have ascertained that they
belong to the sexual generation o( Aphilotrix autumnalis,
that is Andricus ramuli.

[The autumn gall is found in October on Quercus sesstlijiora and
Q. pubescens.

Inquilines. Sytiergus nervosus, S. variolosus, S. rnficornis, and
S. apicalis.

Parasite. Megastigntus dorsalis.'\

13a. Andricus ramuli. L.^
Gall. This gall, which very frequently developes from
the male flower-buds but occasionally from the leaf-
buds, resembles a ball of cotton-wool and varies in size,
the size depending on the number of single galls in the
conglomeration. On transverse section we find an
aggregation of small oval galls 2 mm. long, each of which
bears a very long tuft of pale yellow hair. These hairs
are interwoven so as to resemble a thick white felt and
this gives the gall a very dainty appearance. (Fig. 13^^.)
The fly emerges in the first half of July-
Fly. 2 mm. long ; entirely yellow, with the sutures of
the thorax somewhat darker; in the female the back of
the abdomen is brown, in the male black ; the antennae
and legs are uniformly yellow.

[' Teras amen/orum, Htg. Cynips quercus-ramuli, L.J

6o Observations on Cynipidae.

Experimental breeding. As Andricus ramuli galls
occur here very seldom I have only once been able to
make observations on the propagation of the flies. On
July 9, 1878, I found several of these flies pricking
axillary buds. I marked six of such buds with threads
and from two of them in the beginning of October galls
of Aphilotrix autumnalis developed.

[The woolly or cotton gall is found in May and June on Qucrcus
pedunculata, Q. sessilijlora, and Q. pubescens.

Inquilines. Synergus facialis, S. radiatus, Ceroptres arator, and
Didyopteryx Loeflingiana.

Parasites. Olinx gallarian in June, O. debilis, Toryniits aura/us,
Decatonia Neesi, Eurytonia seniirufa, Pteronialiis Ratzeburgi, Anihomyia
{Honialomyia) canicidaris. ]

III. Dryophanta Group \
14. Dryophanta scutellaris. Htg.^

Gall. This gall is globular and is always found on
the under surface of the leaf. It varies greatly in size
and may attain to 2 cm. in diameter. The gall always
springs from the veins of the leaf and more frequently
from the midrib than from the lateral veins ; but it is
only connected with the vein by one point, so that on
looking down upon the upper surface of the leaf its
presence cannot be recognized. The gall is of a white
or yellow colour, the side exposed to the sun being of
a beautiful red. It appears in the beginning of July,
and matures in October. (Fig. 14.)

The fly is easy to rear from the gall, but reports as to
the time when it emerges differ. According to some

[^ Dryophanta, Foerster. Liodora, Foerster.

2 Cynips Quercusfolii, Lin. Diplolepis scutellaris, Oliv. Cynipsfolii,
Hartig. Cynips scutellaris, Schenck.]

Dryophanta scutellaris. 6i

observers the flies appear in October, and according to
others not until March. To ascertain the natural time
of emergence the galls must be kept in the open air; if
they are kept in a room undoubtedly the flies appear in
November, but this is not the case if they are kept
in the open air. The fly certainly begins in October or
November to gnaw a passage from the central chamber
in which it lies, towards the periphery, but it does so
without quitting the gall. On the contrary the fly allows
a thin lamella of the outer rind to remain, but so thin is
this layer that the lumen of the passage can be seen
through it. Yet weeks may still pass before the fly
breaks through this slight barrier and emerges from the
gall ; this depends entirely upon the weather. If, for
example, in December there should be a hard frost, the
fly remains within the frozen gall, but as soon as a thaw
comes it releases itself, probably because in thawing the
gall quickly perishes. I have repeatedly noticed that
the warmer days and thaws of January entice the flies
out ; but when the frost lasts through January the flight
of the flies is delayed until February, or even later
should the frost continue. In this case many flies do
not appear until March.

Ply. Size 4 mm. long ; black ; vertex of head
reddish brown, as also are the sides of the thorax and
sometimes the scutellum ; abdomen jet black and ver^^
shining ; legs black except the lower half of the femora
and the upper parts of the tibiae which are reddish brown ;
the wings are long and the whole insect very hairy, the
long hairs standing out from the legs and antennae are
characteristic ; the antennae have thirteen joints.

62 Observations on Cynipidae.

Experimental breeding. In the year 1876 I made
experiments with this fly which showed me that it
pricked by preference the Httle adventitious buds on
the trunks of the older oak trees. My first attempts
were only made with a few flies in the open air, and
the results I then obtained proved later to be incorrect.
I repeated the experiments on a larger scale in 1878.
I had kept a large quantity of galls out of doors through
the winter, and in January the flies began to take flight.
I put them on a little oak indoors and observed that
after a few days they began to oviposit, choosing the
little adventitious buds that were on the stem. The
buds were pricked in the following manner. The fly
reared itself, directing its ovipositor to the point of the
bud, and bored down into it perpendicularly. The fly
is armed for this purpose with a tolerably straight and
strong ovipositor. Some time is required to complete
the act of ovipositing and the fly usually spends half an
hour in the pricking posture. In each bud, only one
egg is laid. If a pricked bud is examined it will be
seen that the egg lies at the base of the bud-axis, in the
cambium layer which is continued into the bud, there-
fore it may be predicted with certainty that a bud-gall
will be the result. In my experiments thirty-four buds
were pricked between January 20 and January 26,
but it was not until the end of April that I was
able to observe the beginning of gall formation in any
of the buds. The points of the buds became dark blue
and soon the dainty velvety galls of Spathegaster Tas-
chcnbergi became evident ; by the beginning of May
eleven galls developed on the tree. In the year 1879

Spathegaster Taschenbergi. 6-^

I repeated the experiments and again obtained Spathe-
gaster Taschenbergi galls.

[The cherry gall is found in July on Quercus sessili/lora, Q. pedun-
culata, and Q. pttbescens.

Inquilines. Synergus vulgaris, S. pallicornis, in the spring of the
second year ; 5. Tscheki, Sapholytus connatus, and Neuroterus parasiticus.

Parasites. Syntonxaspis lasulina, May and June of second year ;
Torymus abdontinalis, in March of second year, T. elegans, T. incertus,
T. regius, and Callimonte antennatusir om March to June of second year.
(This last species is sometimes hyperparasitic on the Inquilines.)
Eurytonia nodularis, E. setigera, E. rosae, Megastigtnus dorsalis, Porizon
claviventris, Bracon aterritttits Orihostigma gallarutn, Pieroniahis
fasciculatus, P. jticundus. Decatoma biguttata.'\

14^. Spathegaster Taschenbergi. Schltdl. ^
Gall. These dainty little galls measure 2-3 mm. in
length; they have a velvety rind with a rounded point
of a dark violet colour ; this beautiful colour is caused
by a peripheral layer of pigment cells, studded over
with short white hairs which give the velvety appearance
to the surface. The inner kernel of the gall is soft and
consists of cells containing starch granules ; these are
completely eaten up by the larva, so that ultimately
nothing is left but a thin rind. (Fig. 14^.) To rear
the flies the galls must be collected in the beginning of
May and kept in damp sand ; the flies appear in the
end of May or the beginning of June.

Fly. Size 2-5 mm. long; antennae, head, thorax
and abdomen black ; thorax smooth and very shining,
scutellum dull and not haired ; legs yellowish, only
trochanters black, wings long and smoked. The male
and female similar.
Experimental breeding. Immediately after fecunda-

[* Dryophanta Taschenbergi, Mayr.]

64 Observations on Cynipidae.

tion the females begin to lay their eggs. In May, 1878,
I experimented with the oak, on which the Spathegaster
Taschcnhergi galls had been formed. The first flies
appeared on May 26. Before a fly begins to prick, it
may be seen busily engaged in feeling the veins of the
leaf with its antennae, and having done so it pierces
them, so that the eggs lie in the veins of the leaf. It
is essential if the experiments are to succeed that the
leaves should be very soft and tender, for full grown
leaves do not seem to suit the fly. Only five leaves
were pricked in my experiments because some were
already too far developed.

In the beginning of July I noticed the commence-
ment of gall formation as a small round gall growing
from the midrib of a leaf. Others soon followed, and
I obtained in all eight galls which proved to be those of
Dryophanta scutellaris.

The connexion of Dryophanta scutellaris with Spathe-
gaster Taschenbergi was thus proved. The statement
made in my first communication that Trigonaspis crus-
talis was the sexual generation belonging to Dryophanta
scutellaris was due to a mistake, which arose from my
having made my experiments in the open air where
I was not sufficiently able to control them.

[The purple velvet bud gall is found in April on the dormant buds
of Qitercus sessiliflora.']

15. Dryophanta longiventris. Htg.^
Gall. This gall like the former one grows from the
midrib on the under side of the oak leaves, but is smaller,

[^ Cyuips longiventris, Htg.J

Dryophanta longiventris. 6^

being at most i cm. in diameter. It is brilliantly
coloured, prettily striped with white and red, and the
outer rind is smooth or somewhat nodulated. (Fig. 15.)

Rearing the fly is simple if the galls are collected in
October when they mature. I have obtained the flies at
the end of November and in December. Although the
gall is not scarce, it is difficult to obtain any large number
of flies, as most of the galls are infested with parasites.

^y- 3~4 mm. long ; black ; the margin of the orbits,
sides of the thorax, two stripes on the meso-thorax, and
the scutellum are reddish brown ; abdomen black and
very shining ; legs reddish brown, trochanters and upper
halves of the femora black ; the pubescence is the same
as in Dryophanta scutellaris, from which it cannot in
other respects be distinguished with certainty.

Experimental breeding. On account of the small
number of these flies procurable, I had great difficulty
in getting any results from experiments. In November,
1877, I put several flies on a little oak and observed
that, like Dryophanta scutellaris, they sought out the
younger adventitious buds and pierced them. It was
therefore probable that a similar bud-gall would be
formed, but the result was negative, for I obtained no
gall. My second experiment, made in 1878, was also
negative. For the third time, I tried to secure a gall
in November, 1879 ; several buds were pricked and I
succeeded in April, 1880, in obtaining two galls. They
were very like those of Spathegaster Taschenbergt, but
with care it was not difficult to distinguish between
the two. This result was the more interesting because
it was now clear to me that I had hitherto mixed up

F

66 Observations on Cynipidae.

this undescribed species with Spathegaster Taschenbergi.
In 1876 (when I did not know the connexion that ex-
isted between the last two species) I obtained, from an
experiment I then made, galls of Dryophanta longiventris
upon leaves which I believed had only been pricked by
Spathegaster Taschcnbeygi. Among the collected Spathe-
gaster Taschenbergi galls I ought to have observed that
there were some of which the colouring was different ;
these resembled the galls which I now obtained from
my experimental breeding with Dryophanta longiventris.
This gall, which I am now about to describe, is that
of Spathegaster similis.

[The striped gall is found in July on Qiteirns pcdnncidata. When
attacked by inquilines it often remains very small.

Inquilines. Synergiis pallicornis and S. apicalis.

Parasites. Syntotnaspis cyanca, S. lazulina, Toryinns abdojninalis
and T. regius, Callimome longiventris, Elachestus cyniphidiittn.'\

15'\ Spathegaster similis. n. sp,^
Gall, About 2 mm. long ; like Spathegaster Taschen-
bergi but more slender and pointed ; of greenish grey
colour and with a velvety rind. The colour is caused
by a peripheral layer of cells containing a greenish
pigment, but this tint is rendered dull by a covering of
long white hairs, imparting to it a grey tone. It
is especially the stronger and longer pubescence which
is the important distinction between this and the
Spathegaster Taschenbergi gall. (Fig. 15 ^.)

These galls are found almost exclusively on the
adventitious buds at the base of old oaks ; but it may

' So called on account of its close resemblance to the Spathegaster
Taschenbergi gall.

Dryophanta divisa. 67

happen that they grow out of the buds of last year's
shoots, and then they are not unfrequently formed on
the trunk of the tree.

That the two species of Dryophanta just described
should both seek the little adventitious buds at the
foot of the oak, is probably due to the fact that these
buds are the first to be reached in spring by the rising
sap, and therefore they are able to support gall forma-
tion while the higher buds are still dormant. It is of
advantage to the summer generations of Dryophanta
that their flies should be enabled to leave the galls as
early as possible, since by doing so they are the
sooner safe from the attacks of parasites. The flies
emerge from Spathegaster similis galls in May, almost
a fortnight earlier than from Spathegaster Taschenbergi
galls.

Ply. 2 mm. long ; black, sufficiently like Spathegaster
Taschenbergi to be confused with it, and only to be
distinguished from it by the darker colouring of the
legs ; these are dark yellow, the outer margins of the
femora and tibiae black.

[The green velvet bud-gall is found on dormant buds of Qitercus
pedunculata in April.]

16. Dryophanta divisa \

Gall. Of the size of a buckshot ; several are usually
found together on the under side of the leaves, springing
from the veins of the leaf; at first of a bright red
colour but this at maturity passes into a brown. The

\} Cynips divisa, Hartig.]
F 2

68 Observations on Cynipidae.

gall appears at the end of June and ripens in October.
(Fig. i6.)

Fly. The flies are from 4 to 5 mm. long ; brownish
red, with antennae, sutures of the thorax, two stripes
on the mesothorax, and the back of the abdomen black ;
the legs are brown, the trochanters and tarsal segments
partly black ; pubescence the same as in Dryophanta
scutellaris. The fly usually emerges at the end of
October or beginning of November and sets to work at
once to prick the buds. This is another confirmation
of a rule that holds good without exception, that gall-
flies begin to lay their eggs immediately after leaving
the galls, and that no fly passes the winter outside the
gall to lay its eggs in the buds early next Spring. With
this fly I have made many experiments.

Experiments in breeding. In October, 1877, I placed
several flies on a little oak and covered it over. In the
beginning of November I noticed that the flies were
pricking the buds. Unlike the two former species of
Dryophanta they did not choose the little adventitious
buds, but selected the large terminal ones. The ovi-
positor was applied as before to the point of the bud,
and bored perpendicularly into it. On examining
a pricked bud I found two eggs laid on the rudimentary
leaves. I knew therefore that more than one egg was
laid in a bud, and I was enabled to predict that the galls
would be formed on the leaves. But this prediction
was not yet to be confirmed, for I obtained no galls.

In the year 1878, I repeated the experiment; after
anumber of flies had been enclosed, they began to prick
the buds on October 28. The flies remained alive

Spathegaster verrucosus. 69

about fourteen days and pricked a series of buds during
this time. After their death I took the oak out of
doors for the winter, but next year in the beginning
of May, when the buds began to shoot, I brought
it indoors again for more convenient observation.
When the leaves unfolded, dainty little galls appeared
upon them, five in all, besides one which grew
directly out of a bud. This gall, produced by Dryo-
phanta divisa, is that of Spathegaster verrucosus.

[The scarlet pea gall is found in June on Querctis pedunciilata.

Inquilines. Synergns pallicornis, in April of the second year ;
5. Tschcki, in March of the second year ; and S. albipes, in August of
the same year.

Parasites. Synioynaspis cyanea, in spring of the second year;
5. lasulina, Torymus abdoniinalis, T. pubescens. T. regius, Pterontalus
Saxeseitii. P.fascicidata, all in autumn of the same year ; P. incrassatus,
in May of second year ; Eurytonia squantea, E. setigera, E. signata,
E. rosae, Decatoma biguttaia, Eiipelmus urozonus?\

\Q^. Spathegaster verrucosus. Schltdl. ^

Gall. About 4 mm. long ; oval in form, with broad
rounded point ; of a greenish yellow or somewhat
reddish colour ; with a peculiar granular but rather
glossy rind, caused by the peripheral cells bearing,
instead of hairs, small round bladders filled with a clear
fluid, probably a protection against parasites. The
situation of the galls is peculiar because they grow
sometimes on the leaves, sometimes on the shoots, and
sometimes from the buds ; this is due to the fact that
although as mentioned above the egg of Dryophanta
divisa is usually laid on the rudimentary leaves, yet

[ ' Dryophanta divisa, sexual form, Cameron. Dryophanta verrucosa,
Mayr.]

70 Observations on Cynipidae.

in some cases it may come to lie in other situations.
A slight pushing of the egg higher up or deeper down
makes all the difference as to the position of the gall.
If the egg lies on the point of a leaf, the gall developes
on that spot, and the full grown leaf bears a gall on its
point; but if the egg lies deeper in the base of the
leaf, the whole leaf-surface is absorbed, and the gall
rests directly on the shortened petiole. It may appear
sometimes as if the gall had sprung from the shoot
itself, but in the angle which it forms with the shoot
there is always a little axillary bud, a proof that the
gall is merely substituted for the leaf. Lastly, when
the egg is sunk still deeper into the axis of the bud,
the whole bud is absorbed in the gall formation, or in
other words a bud-gall is formed. These different
varieties are illustrated. (Fig. i6^.)

The gall matures in the end of May and the flies
emerge in the last days of May or in the beginning of
June.

Fly. Size 3 mm. long ; black ; thorax smooth and
shining, the sides only faintly punctate, the scutellum
rough, on the metathorax a scanty white pubescence ;
abdomen brilliantly jet black ; legs orange, trochanters
black ; males have similar colouring, but darker legs.

No experiments have been made with this fly, but
as the formation of the gall by the agamous generation,
Dryophanta divisa, has been established, there is no
doubt that Spathegaster verrucosus is the sexual genera-
tion belonging to it.

[The red wart gall is found in May on Qitercus sesstli/lora.']

Biorhiza aptera. 71

IV. Biorhiza Group \
17. Biorhiza aptera. Fbr.-

Gall. This gall is formed only on oak roots, and on
the smallest as well as on the thickest. When it first
bursts through the cortex it is soft and of a pink colour,
but at maturity it becomes brown, hard and woody.
The galls vary much in size, the smallest being about
the size of a pea. They are rarely isolated, and are
usually united into a large mass. (Fig. 17.)

Owing to their obscure situation it is not easy to
procure the galls, but the flies may be collected when
they appear on the oak. The time given by different
authorities for their appearance varies, some having
found them in November, and some in March ; according
to my own observations the latter date must be con-
sidered as exceptional, at least in this place. I have
for many years found the flies regularly in the end
of December and beginning of January.

Fly. Size 4-7 mm. long ; wingless ; thorax slender,
pilose at the sides ; the whole insect yellowish brown ;
the abdomen darker, with an almost black transverse
band across its middle ; legs of same colour ; size of the
fly very variable.

Experimental breeding. I have made many attempts
at breeding with Biorhiza aptera, and I was very soon
satisfied that the flies do not go to the roots of the oaks
to deposit their eggs, but rather try to ascend by

[ * Biorhiza, Westwood. Apophylliis, Hartig. Teras, Hartig. Dryo-
teras, Foerster.

* Cynips aptera, Fab. ; Biorhiza terminalis, agamous form, Cameron.]

72 Observations on Cynipidae.

creeping up the trunks. They then seek by preference
the greater terminal buds, and begin to bore into them.
The pricking is done in a very different way from that
of other gall-flies. After a suitable bud has been found,
the fly stops, turns with its head downwards, and
directs its abdomen to the point of the bud. In this
position it inserts its ovipositor somewhat below the
middle of the bud, and bores straight towards the base.
The egg comes to lie deep in the bud, in or upon the
tissue from which the terminal growth proceeds. After
the fly has pushed in its ovipositor it withdraws it, and
goes on boring one canal after another in the stratum
which the egg is to occupy, until the whole layer is
riddled like a sieve. When the operation is finished,
the eggs are successively pushed into the pricked
canals, where they lie so thickly together that they
look like a continuous mass. The amount of work
which the fly goes through in laying its eggs in this
way is astonishing. After having been occupied for
hours in boring these numerous canals, it appeared
to me at first inexplicable that it had as yet laid no
eggs ; I found, however, that it bores all the canals
for their reception before actually laying a single egg.
This part of the work requires much time, as to which
I have made the following observations.

On January 27, 1878, a fly was put upon a little oak,
and soon began to prick a bud ; when it had finished
the first bud, it went on without interruption to another,
and was altogether eighty-seven hours busily employed
in laying its eggs. In these two buds I counted
582 eggs.

Teras terminalis. 73

For actual breeding purposes I allowed the flies to
pierce two little oaks ; on these they pricked six buds.
In the beginning of May two buds showed evidences
of gall formation : at the base of the bud a swelling
formed rapidly, and the real bud seemed to be
absolutely raised and set loosely on the gall, a proof
that gall formation springs from the meristem at its
base. At the end of May the galls were fully grown,
and proved to be those of Teras terminalis^ . Whether
the experiments w^th Biorhiza aptera are made indoors
or out, it will always be found that in many of the buds
no gall formation occurs : the reason of this being that
the ovipositor of the fly causes an extensive destruction
of the tissues of the plant, and if no zone at the germinal
point remains intact, gall formation cannot take place.
The development of the bud is impossible where the
whole bud-axis is cut through.

17*. Teras terminalis. Fbr.'^

Gall. This gall grows, as the name indicates, chiefly
from terminal buds, but sometimes it may be found

^ The connexion of the two generations Biorhiza aptera and Teras
terminalis has also been proved by Dr. M. W. Beyerinck, as I see
in a communication to the Entoniologische Nachrichten, vol. vi.
p. 45 (March, 1880). See Beyerinck, Bijdrage tol de Morphologic der
Plantegallen, Utrecht, 1B77.

[The root gall is found in September and October on Quercus pednn-
culata, Q. sessilijlora, and Q. pitbesccns. The gall lives about fourteen
months.

Parasite. Torynius ttobilis. It is stated by Curtis and others, that
Biorhiza aptera is polyphagus and occurs on beech roots. Cameron,
Hyynenoptera, vol. iv. p. 13.

- Cynips querciis-terminalis, Fbr.]

74 Observations on Cynipidae.

springing from an axillary one. It is spherical, varying
in diameter from 1-4 cm. When fresh it is of a pale
colour often beautifully tinted with rose, resembling
an apple. At first its tissue is soft and sappy, but at
maturity it becomes hard and woody within, while its
periphery changes to a loose spongy mass ; in the
woody kernel lie countless larva chambers. (Fig. 17 '^.)
The gall matures in June, and the flies emerge in July.
Owing to the great abundance of the gall, the flies can
be reared in large quantities without difficulty, although
the galls are much interfered with by parasites,
particularly by the larva of one of the Ciirailionidac,
Balaniniis villosus. I have frequently found this rather
rare beetle in the gall of the Tcras terminalis. It
hollows out a perpendicular channel with its long thin
proboscis, lays an ^^^^, and pushes it down into the
end of the passage. Afterwards, when the larva
escapes from the ^^gy it eats its way through the gall
in various directions ; as it happens that several eggs
are usually laid in a gall, the gall is so completely
wormed through by the grubs, that often not a single
larva chamber remains undisturbed.

Fly. Size 3 mm. long ; of a uniform yellow colour ;
abdomen darker, especially on the dorsum ; the males
are paler in colour, and are winged ; the females are
wingless or with rudimentary wings only.

Experimental breeding. I made my first experiments
in July, 1876. I put a large number of flies on one
of the little oaks under a covering, and observed them
for several days indoors. When the flies began to lay
their eggs, I was at first surprised to find that they

Teras terminalis. 75

pierced not only the bark of the roots, but also the buds
and even the leaf-stalks. To be perfectlysure, I examined
the pricked buds and leaf-stalks, and found unmistakable
bored canals with the eggs in them. When the time of
gall formation arrived, towards the end of August,
I observed bright red galls growing out of one leaf
stalk, several buds, and some spots in the bark of the
root. They grew slowly ; by the end of September
some of the root-galls were from -5 to i cm. in diameter,
but the bud and leafstalk galls were only the size
of a pea. In October these lost their brilliant red
colour, and dried up. The root-galls appeared at
first to pass the winter well, but finally perished, and
I did not succeed in obtaining a single fly.

In July, 1878, I repeated the experiments, and
I obtained some bud-galls, and also some root-galls
which I brought to full development. In October the
growth of the galls ceased ; they were of soft, sappy
consistence, and the larvae were very small, but next
spring they came to their full growth, and began to get
woody. By an unlucky chance I obtained no flies from
these galls. This experiment was interesting, as it
confirmed my previous observation that Teras terminalis
pricks buds. To consider this as a mistaken instinct,
appears to me erroneous ; I rather incline to the view
that in the phenomenon we have a peculiarity trans-
mitted from the apterous generation. The two genera-
tions are so remarkably alike, that with the exception
of the presence of male flies in Teras terminalis no
distinction can be found, the female flies being exactly
similar ; and their close relationship is still further

y6 Observations on Cynipidae.

shown by the fact that in Teras terminalis some flies
preserve the habit of pricking buds like their mother
flies. Here the great resemblance of the two flies,
in spite of their different development and manner of
life, is striking \ Since Biorhiza aptera is wingless, it
need cause no surprise that the Teras terminalis
generation is also deficient in wings, for we must
remember that although the males are always provided
with perfect wings, yet the females are either wingless
or have short rudimentary wings only. Are these
rudiments to be considered as organs in the process
of development or of degeneration ? I believe that
the decision must depend on whether the possession
of perfect wings would be more advantageous than
the present rudimentary ones. It must be apparent
to anyone who watches the flies while pricking, that
perfect wings could be of no great use to them. The
fly does not need wings to reach the place where it
is to lay its egg, as it has only to creep down the trunk
to get at the roots ; but having done this it has in
addition to penetrate the ground, which it accomplishes
by pushing its way backwards with the aid of its abdo-
men. In the act of burrowing, wings could only be
a hindrance, therefore the apterous condition is a decided
advantage to the fly.

There is a curious phenomenon in the propagation of
Teras terminalis which deserves notice. It appears that
while some galls produce both sexes, some yield only

[' Another point of resemblance is found in both generations
possessing a disagreeable bug-like smell, which is probably defensive
in character, as it persists after ovipositing is over.]

Teras ierminalis. 77

females, others only males. It seems probable also
that some specimens of Biorhiza aptera produce only
males and some only females. We are therefore driven
to admit that the sexes are differentiated in the egg,
and that this phenomenon cannot be referred to any
other influence, such as different or more abundant
nourishment of the larvae.

[The oak apple is found in May on Qticrciis pcditnatlata, Q. sessih-
flora, and Q. pubescens. According to Mayr, the gall-makers, as well
as the inquilines and some parasites, make their appearance in the
end of May or the beginning of June. In June the Rosechafers
{Cetonid) eat their way into these galls, consuming the outer spongy
tissue, and leaving the inner cells adherent to each other. From
these inner cells parasites are produced in the second year. A large
caterpillar, probably of a Noctua, sometimes consumes the whole
interior of the oak apple.

Mr. Francis Walker gives the following list of insects inhabiting
oak apples : —

June (1845'!. Nitidula grisea, Balaninus glandiunt, Forficttla ami-

cularia, Psocus stibocellatus, Atropos ?, Synergus socialis, and

specimens of two or three other species of Cynipidae, Pteroinaltis

Naubolns, Pteromalus ?, Pteromabis semifascia, Pteromalus ovatus,

Pteromalus domesttcus, Etipcbnus urosonus, Etdophus gallarum, Ceci-
domyia 2 sp., Toririx viridana.

July. PJiysoev7-ia ?, Nitidida grisea, Lairidius lardanus, Coiii-

caria fransversalis, Carpalimus fidiginosus, Aleochara ?, Orchestes

quercus, Pimpla 2 sp., Hentiieles arcator, Synergus socialis, Decatoma
immaculata, Megasfigtnus dorsalis. Callitnome cingtdatus, viridissimus ,
parellinits, inconstans, confinis, ntinutus, exilis, chlorinus, nndabilis,
latus, leiicopterus , abdominalis, leptocerus, autuntnalis. Pteromalus
Naubolus, dilectus, fuscipennis, fasciiventris, ovatus, hilaris. Eupelmus
urosonus. Tetrastichus diaphantes. Eulophus gallarum, Agathyllus

? sp. Inostemma Boscii. Ceraphron ?. Drosophila ?. Lozo-

taenia xylosteana, Zeiraphtra comntunana. Chaetochilus sylvcllus.
Pentatonia lurida. Aiithocoris nemorum. A few Arachnidae and
.^ca« of such species as dwell under the bark of trees.

August. Drotnius quadrimaculatus. Cryptophagus cellaris. Corti-

caria fransversalis. Microgaster ?. Aphidius ?. Synergus

socialis. Decatoma immaculata, Megastigmus dorsalis. Callimome,

78 Observations on Cynipidae.

same species as in July. Enpelmus urosonus. Tetrastichus diaphantes.

Chactochilus sylvelltts. Aphis ?. Thrips ?. Pteromalus

Naubolus, dilectus, fuscipennis, platynottis, planus, dubius, fasciiventris,
decidens, ovatus.

September. Cryptophagus cellaris. Latridius transversus, Corfi-
caria tratisversalts. Megastigntus dorsalis, Callimome, same species as
in July. Pteromalus Naubolus, dilectus, decidens, ovatus, and two
doubtful species. Eupelmus urosonus. Ceraphron, two doubtful
species.

October. Megastigntus dorsalis. Pteromalus dilectus, ovatus. Tetra-
stichus diaphantes.

December. Megastigmus dorsalis. Callimome nigricornis.

January (1846). Same.

February. Same, and Pteromalus domesticus. Eulophus gallarum.

March. Bracon ?. Synergus socialis. Callimome nigricornis.

Pteromalus domesticus. Eulophus gallarum.

April. Synergus socialis, S. facialis. Megastigntus dorsalis. Calli-
mome nigriconiis. Pterontalus Naubolus. Eidophus gallarum.

May. Same, and Pteromalus ovatus.

June. Megastignitis dorsalis. Pteromalus Naubolus, ovatus. Eupel-
mus urosontis. Tetrastichus diaphantes.

From a number of Teras terminalis galls, Mr. Walker collected more
than 55,000 specimens belonging to 75 species distributed as follows.
Coleoptera 9 species, 191 specimens ; Orthoptera 1 sp., 5 specimens ;
Neuroptera 2, sp., some hundreds of specimens ; Hyntenoptera (Cyni-
pidae) 4 or 5 species, 30,246 specimens ; Hyntenoptera (parasitic)
45 sp., 24,417 specimens; Diptera ^ sp., 23 specimens; Lepidoptera
5 sp., 9 specimens; Hemiptera 5 sp., 51 specimens; Arachnidae and
Acari 5 or 6 sp.

All the Coleoptera, Otihoptera, Neuroptera, Diptera, Lepidoptera,
Hemiptera, and Apiera, with the exception oi Balaninus glandium and
Drosophila, were probably accidental visitors.

See Wa\kev, Zoologist, iv. pp. 1454-57 (1846); Entomologist, v.
p. 432 (1871), and ix. p. 29 (1876).

Mr. Cameron has only met with one inquiline, S. facialis, and g\v&s
the following list of parasites bred from Teras terminalis : —

Torymus abdontinalis = cingulafus — cyniphidum. T. regius = in-
constans. T. longicaudis = leucopterus. T. auratus = viridissimtts =
autumnalis = confnis = mutabilis = leptocerus = minutus = niuscantnt =
propinquus = nanus = appropinqitans = gallarum.

Syntomaspis caudata = crinicaudis.

Megastigntus dorsalis = Bohenianni = xanthopygus.

Biorhiza retnim. 79

Euryioma rosae.

Decatovna higuttata, D. ininiaculata, D. signafa.

Eupelmus urosonus.

Olinx scianeurus = enedoreschus.

Eiilophns gallariim, E. agathyllus, E. ramicontis.

Tetrastichus diaphantes.

Pteromalus ("Walker's list), P. cordaini, P. meconotus, P. stenonotus.

P. leucopeeus, P. gallicus, P. Dufonrii.

Platynicsopus Westwoodi, P. Erichsoni.

Dendroccrus Lichtenstcinii.

Inostemma Boscii.

The following probably hyperparasitic : —

Piitipla calobata, P. caudata, P. alternans.

Hemitelcs areator, H. coactus, H. piinctatus.

Lampronota segmentata.

Cfyptus Jiorttdanus.

Bracon caudatus,

Apanieles breviventris.

Microtypus Wesmaelii.

Microdtts rufipes.

Ratzeburg gives also : —

Entedon amethystinns, E. deplanatus, Getitocerus cyniphidmm, Eupel-
mus asureus, Mesopolobus fasciiveniris, Torymus admirabilis, T. in-
certus.']

18. Biorhiza renum. Htg.^
Gall. These little kidney-shaped galls, generally
found in great numbers on the under side of the leaves,
are arranged in rows attached to the veins. The
gall is of a green or yellowish colour sometimes tinted
with red. It is formed in September, attains maturity
in October, and then falls to the ground. (Fig. 18.)

Notwithstanding the enormous abundance of the galls,
attempts at rearing do not always succeed. When the
galls fall in October, the larva has not attained its full
growth, and they must therefore be kept on damp sand.

[^ Trigonaspis ruegaptera, agamous form, Cameron. Trigonaspis
renum, Mayr.]

8o Observations on Cynipidae.

When they have acquired by degrees a dark brown
colour, we may consider that larval growth within them
is complete, but the galls must still be left the whole
winter in the open air. The larva then passes the
following year as such, and in October assumes
the pupa state. The flies appear in December and
January, but there is always a fair proportion of galls
from which insects do not emerge until the third year.

My. Size 1-5 mm. ; wingless; the whole fly brownish
red ; legs light yellowish brown ; thorax dull and
punctured ; scutellum hairy ; abdomen almost sessile
and very shining, vertex finely shagreened, in the
middle line a shallow furrow with a little protuberance
on each side. Antennae of thirteen joints, labial
palpi of two joints, maxillary palpi of four joints.

Experimental breeding. I could not at first discover
where this species laid its eggs. It was very certain
that the insect which emerges in January could not
be the author of the galls of Biorhiza rcnum formed
on the leaves in September. A consideration of the
structure of the ovipositor would lead one to imagine
that the insect punctures buds, but I could not at first
succeed in seeing the fly lay its eggs. In December,
1878, I reared a certain number of flies which I placed
upon a little oak. At first they remained perfectly still,
then they began to move about, and feel the adventitious
buds on the stem with their antennae. At last they
pierced a few of the buds, and at the end of April in the
following year a little red gall, which I soon recognized
as that of Trigonaspis crustalis, grew from two of
these buds.

Trigonaspis criistalis. 8i

[The kidney gall is found in September. This gall grows only in
the shade, and on the north side of trees of Quercus pedunculaia,
Q. sessiliflora, and Q. pubescens.

Inquilines. Synergus varitts, S. vulgaris, S. tibialis, S. ruficornis,
S. pallicornis, and S. Thauniacera, in April of second year.

Parasites. Callintome fuscicrus, Mesopolobus fasciiventris, PterO'
mains Saxesenii, Pleurotropis cyniphidiunt, Anthotnyia gallarum.']

18*. Trigonaspis crustalis. Htg. ^

Gall. These round, sappy, red and white galls vary
in size from that of a pea to a cherry. They are found
most frequently low down on the trunks of old oaks,
often crowded together, but they also occur on small
last-year shoots. The gall always grows out of a bud,
and it is therefore not a bark gall. On old oaks it is
often found quite hidden under moss, so that it certainly
appears then to grow directly out of the bark, but this is
not the case. If the base of the gall be examined, it will
be found invariably to originate in a bud. (Fig. i8^.)

To rear the Fly, it is necessary that the galls, which
are very succulent, should be gathered at the end of May,
shortly before maturity. Most of the flies emerge from
the beginning to the middle of June.

Fly. Size 4 mm. long ; head and thorax black ;
abdomen bright orange, blackish at the apex only,
shining, distinctly pedunculate, and of a rounded form ;
legs orange ; wings very long ; males and females
similar in colouring; antennae of the male 15-jointed,
of the female 14-jointed; labial palpi 3-jointed, maxillary
palpi 5-jointed.

Experimental breeding. I had repeatedly watched

P Cymps megaptera, Pz. Trigonaspis crustalis, Htg. T. megaptera,
Mayr. Cynips crustalis, Thorns.]

G

82 Observations on Cynipidae.

this fly ovipositing in the open air before I succeeded
in being quite certain what gall it produced. From the
structure of the ovipositor resembling that of Spathe-
gaster Taschenbergi, I suspected that it too pricked
leaves. At length I observed in June, 1876, several flies
pricking the veins on the under sides of oak leaves :
I was deceived by an unfortunate accident, and led to
assert that Trigonaspis crustalis produced Dryophanta
scutellaris galls, which also occur on leaves ^ In the
year 1878, I made a successful experiment in breeding
on isolated oaks with Trigonaspis crustalis. It is not
difficult to make the flies oviposit provided we have an
oak with quite tender leaves at our disposal. The flies
do not touch full-grown leaves, they only select those
with veins still soft and tender. They usually prick the
leaves in the evening, or in deep shade in daytime.
The fecundation of the females must first take place.

If the fly is going to oviposit, it can be recognized at
once by the characteristic position it assumes ; first it
wanders over the under surface of the leaves, incessantly
using its antennae, at last it stops, directs its abdomen
almost perpendicularly towards the angle formed by
the vein of the leaf with the leaf-surface, and then cuts
into the side of the vein. Trigonaspis crustalis makes
a whole row of punctures into a single leaf, and the
wounds in the veins can be plainly distinguished after-

^ On June 24, 1876, several leaves were pricked under my eye by
Trigonaspis crustalis. In July, Dryophanta scutellaris galls were
formed upon them. These same leaves had also been pricked by
Spathegaster Taschenbergi, and as I had omitted to examine them again
later, I did not know that other galls were forming there.

Trigonaspis crustalis. 83

wards. I allowed the flies from June 6 to 12 to
prick indifferently two little oaks, one of which I then
kept indoors, and the other out. The next two months
passed without any trace of gall formation being dis-
cernible. At the end of August I examined some of the
leaves, and found eggs in the scars of the punctures
which were still visible ; these contained living and
moving embryos. At last, on September 6, there
appeared simultaneously out of several leaf-veins
little whitish galls which grew very slowly, and three
weeks more elapsed before they could be positively
recognized as those of Biorkiza renum. On one oak
sixty, and on the other about seventy galls were formed.
The observation of the generation-cycle was thus
complete.

On account of the morphological features of interest
which these two generations offer, I have given a draw-
ing of both flies. (Fig. 18-18 **.)

A comparison of the two generations shows some very
striking differences : the form, size, and colouring are
utterly unlike, and the variation extends to other parts
of the body. In Trigonaspis crustalis the antennae are
respectively 14 and 15-jointed, the maxillary palpi
5-jointed, and the labial palpi 3-jointed. On the other
hand, in Biorhiza renum the antennae are 13-jointed, the
maxillary palpi 4-jointed and the labial palpi 2-jointed.
Lastly the ovipositor is of a totally different construction
(see illustration, PL III. 6, 6*). Owing to these and
other important differences, the two generations would
undoubtedly have been considered as belonging to
different genera.

G 2

84 Observations on Cynipidae.

[The pink wax gall is found in May on dormant buds of Quercus
sessiliflora and Q. pubescens.

Inquilines. Synergus ihaumacera in June and July of same year;
Synergus facialis, S. erythrocerus, and 5. pallicornis.

Parasites. Torymus amoenus, T. flavipes, Syntomaspis fastuosa,
Callimome rubriceps, and Limneria exareolata. Birds frequently pick
the larvae out of these galls.]

19. Neuroterus ostreus. Htg.^
Although I have not succeeded in fixing the genera-
tion-cycle of this fly, it appears to me desirable to
include a notice of this species. Until now it has been
classed with Neuroterus, but it differs so materially from
the species o^ Neuroterus before described that I propose
to separate it from them.

Gall. This dainty little gall is spherical ; 1-2 mm. in
diameter ; grows generally from the midrib on the
under side of the oak leaves, and is at first enclosed
between two brownish scales. Later it grows beyond
the scales which then fall off; it is of a pale yellowish
colour, very often marked with red spots. The gall
appears in August and September, and when mature
falls to the ground. (Fig. 19.)

When the gall becomes detached from the leaf, the
larva is still small ; it is therefore necessary to keep the
galls for some time on damp sand. I have had some
difficulty in rearing any considerable number of these
flies, because as a rule the great bulk of the galls are
beset with parasites. Meantime, however, I have ascer-
tained that the flies appear at various times. In galls
maturing early, larvae are full grown at the beginning of
September, and the flies emerge towards the end of

[1 Andricus ostreus, Mayr.]

Neuroterus ostreus. 85

October, in the same year. On the other hand, those
galls which mature in October do not yield their flies in
the same year, but these pass the winter in the pupa
state, and appear next March.

Fly. Length 2-5-3 mm. ; black ; thorax dull, thinly
covered with whitish hairs, scutellum rugose ; antennae
black, pale at the base ; legs uniformly orange.

Attempts at breeding with this fly have been made
without any results. I succeeded in getting some flies,
which were hatched in October, 1878, to prick the buds,
but no galls were formed. There can be no doubt,
however, judging by the formation of the gall, that a
generation alternating with this species does exist. The
flies emerging in October and March cannot directly pro-
duce the galls which appear in August ; and as these galls
spring from the midrib of a leaf late in the summer, it
is clear that another generation must have laid the egg.
I strongly suspect that the sexual generation belonging
to Neuroterus ostreus is to be sought for in Spathegaster
Aprilinus^, The construction of the ovipositor which is
specially designed for boring the ribs of leaves, and a
certain general similarity in the flies, bear out this view.

[' Professor Mayr informs me that this conjecture has since proved
to be correct. Beyerinck, however, describes a sexual generation
inhabiting a small bark-gall growing on the bud-ring which he calls
Neuroterus faninatlus, hut he gives no details. {Beob. iib. d. e. Enttvick.
e. Cynipideii'G alien, p. 37, note.) He also states that he bred Neuro-
terus Aprilinus from the galls of Aphiloirix soUtaria (1. c. p. 138, note) ;
and Schlechtendal and Loew consider that Neuroterus Scldecliiendah
is the agamous form of S. Aprdinus. Neuroterus Schlechtendali is
a small gall, i mm. in length, green at first, afterwards brown,
springing from a dilated part of the catkin in May on Quercus
pedunculata, Q. sessdiflora, and Q. pubescens. It emerges in July of
the second year.]

86 Observations on Cynipidae.

[The oyster gall is found in August on Quercus sessilijiora, Q. pedun-
culata, and Q. pubescens.

Inquilines. Synergtis irisiis in April, and S. Tsclieki in June of
second year.

Parasites. Picrotnalus bisignatus, Eurytoma rosae, Anlax syn-
crepidusJ\

19^. Spathegaster Aprilinus. Gir.

Gall. The galls spring from buds and are of different
sizes. They are round, of a pale or greenish yellow
colour, and are surrounded at the base by bud-scales.
They are very thin-walled and each contains one or
more larva chambers which may sometimes be recognized
through the outer wall. The gall appears in the end of
April or beginning of May, and matures very quickly.
(Fig. 19^)

The fly emerges in the end of May. »

Fly. Length 2-5 mm,; black; thorax somewhat
shining, scutellum wrinkled ; abdomen shining ; an-
tennae black ; legs dark yellow, coxae and basal half
of the femora blackish ; males and females similar in
colouring. I have not succeeded in breeding this fly.

This species is distinguished from the closely allied
Spathegaster Taschenbergt and S. simi'h'shyihe ovipositor
being longer in proportion, pointed, and straight.

[The April bud-gall is found on Quercus pubescens and Q. sessiltflora,
Inquilines. Ceroptres arator in June of the first year. Plaiytnesopus
tibialis in May of the first year.]

In the case of those gall-flies which have hitherto
been described we have observed this curious circum-
stance, that they each possess a regular generation-
cycle, consisting of two forms more or less distinct.

Aphilotrix seminationis. 87

In one generation only females occur, and reproduction
is wholly by parthenogenesis, in the other generation
on the contrary both sexes exist, and parthenogenetic
reproduction is unknown. This alternation of genera-
tions, as it occurs in these species, appeared to me at
first to be the natural and universal rule ; and I believed
that the problem of the position of the so-called agamous
gall-flies would be solved by regarding an agamous and
a sexual generation as forming a connected generation-
cycle. Further observation has however shown me that
the existence of alternating generations is not an absolute
rule applying to all species of oak gall-flies.

Several agamous species of gall-flies still remain to be
described which are not linked to any alternate
generation.

These species are few in number, and propagate them-
selves in an unbroken succession of generations in the
female sex. I add the following descriptions of them
because it is interesting to compare them closely with
the other species. They belong entirely to the genus
Aphilotrix.

20. Aphilotrix seminationis. Gir.^
Gall. Spindle shaped, stalked or sessile, with sharp
or scarcely visible longitudinal ridges; green, often
tinged with red ; at first hairy, especially on the apex,
generally smooth later. The gall occurs on leaves as
well as on the stems of the flowering catkins. When
galls are formed on leaves these undergo striking

[1 Cynips seminationis, Giraud. Cynips inflorescentiae, Schltdl.
Andricus seminationis, ]VIa3'r. Cameron considers the fly indis-
tinguishable from A. quadrilineata^

88 Observations ojt Cynipidae.

deformities, being sometimes deeply indented or dis-
torted. If the galls are formed on catkin stems, these
are often abnormally thickened and remain on the
twigs the whole summer, instead of falling off in the
usual way as soon as the flowering is over. The galls
appear at the end of May, mature in June, and then
fall to the ground. (Fig. 20.) This gall has a strong
resemblance to the Aphilotrix callidoma gall, but is
easily distinguished from it by its point of origin ; it
never grows from a bud like Aphilotrix callidoma.

The rearing of the Fly is accomplished without
difficulty. The galls when collected should be kept
for some time on damp sand, they should then pass
the winter in the open air, and in the following April
the fly will appear. Some galls remain dormant one
whole year, and the fly does not emerge until the second
year.

Ply. Size 3-4 mm. long ; the colour varies from
yellowish brown to dark brown ; the lighter specimens
have on the mesothorax four black lines of varying
breadth, these lines are usually not sharply defined but
somewhat blurred ; in the darker specimens the lines
are scarcely recognizable, the back appearing an almost
uniform dark brown, with the scutellum light. The
sides of the thorax have white hairs, otherwise it is
smooth and shining. Abdomen dark brown above,
with the ventral aspect lighter. The legs vary in
colour from orange to brown, coxae dark, femora and
tibiae black on the outside.

Experimental breeding. I am now enabled to state
the mode of propagation of this species with absolute

Aphilotrix seminationis. 89

certainty, a result obtained by experiments in breeding
carried on for three consecutive years. The flies
emerging in the first half of April soon begin to prick
the buds, and this they do in exactly the same way as
the genus Neuroterus : the ovipositor is pushed under
the bud-scales, glides down to the base, and is then
bored into the interior of the bud ; by this means the
egg comes unfailingly to lie on the rudimentary leaf
In 1876 I made my first experiment; from April 3
to 5 several buds were pricked, and on May 28 two
Aphilotrix seminationis galls were formed. In 1877
seven buds were pricked, between April 13 and 15,
from which I obtained in June four Aphilotrix semina-
tionis galls. And lastly, in 1878, I made experiments
with flies which had been reared from catkin galls, to
convince myself of their indentity with those derived
from leaf-galls ; these flies soon began to prick the
buds of an oak sapling, and the result was that in the
beginning of June, five Aphilotrix seminationis galls
were formed on the leaves. There is this peculiarity
in the growth of these galls, that after the gall has
appeared like a little hairy knob on the unfolding leaf,
there is a long pause in its development, and it is quite
fourteen days before growth begins again. Those
growing on the flower stems have a still longer period
of rest, and in these the first sign of gall formation may
be simply an enormous thickening of the flower stem.

[The barley-corn gall is found in May on Querctis sessiliflora and
Q. pubescens.

Inquilines. Synergus albipes and S. facialis, in July of the same
year.

Parasite. Enrytoma rosae.^

90 Observations on Cynipidae.

21. Aphilotrix marginalis. Schltdl.'

Gall. These conical or oval galls are formed on
leaves, often several on one leaf. They are of a green
colour, or striped with red ; the surface without hairs,
but with irregular longitudinal furrows ; always sessile
and resting on the leaf by a broad base, which indents
the leaf surface. They appear in May and mature in
June. (Fig. 21.)

Rearing the Fly is carried out in the same way
as in the last species ; it appears, like it, in April.

Fly. 2-5-3 n^ni' lorig ; very like the last in colouring.
Some specimens are even darker, they can only be
distinguished with certainty by the galls. Colour dark
brown, the scutellum always pale. The colour of the
legs varies from orange to dark brown.

Experimental breeding. I have repeatedly made
experiments in breeding this fly. The flies emerging
in April soon began to prick the buds, and both in
1876 and 1877 I obtained galls from my experiments.
The first sign of gall formation is a little green, or
occasionally reddish, thickening of the leaf surface,
which quickly grows larger. To enable me more
conveniently to compare the formation of this gall
with the former, I made a combined experiment, in
April 1879, and allowed the last two species to prick
the buds of a little oak together. Several buds were
pricked under my observation by both flies and

[' Cynips marginalis, Schltdl. Andncus tnarginalis, Mayr.
Cameron considers it Aphilotrix quadriliitcaia occurring on leaves
and not a distinct species.]

Aphilotrix quadrilineata. 91

I allowed them to remain for several days. In May

the commencement of gall growth was visible, and

the Aphilotrix marginalis galls were fully grown by

May 30, while the Aphilotrix seminationis galls were

then only visible as little hairy knobs : the much

earlier development of the Aphilotrix marginalis gall

which enables it to arrive at maturity two or three

weeks sooner than that of Aphilotrix seminationis,

serves as a certain distinction between the two galls.

[The marginal gall is found in May on Quercus sessiliflora.
Parasite. Olinx trilineata^

'2i'i. Aphilotrix quadrilineata. Htg.^
Gall. In shape the gall is oval, sometimes almost
round ; it is smooth or irregularly furrowed and ridged,
of a green or reddish colour : it springs usually from
the stalk of the flowering catkin, but, exceptionally,
from the leaves; it appears in May and matures in
June. (Fig. 22.) This gall is so like the last that it
cannot be distinguished with certainty from it, and it is
possibly identical with it. The Aphilotrix quadrilineata
gall grows both from the leaves and flowering catkins
in the same way as the Aphilotrix marginalis and
seminationis galls. Notwithstanding that this gall is
very abundant it is by no means an easy thing to rear
the fly. From the majority of the galls parasites are
usually obtained ; then the larva in a large number of

[' Andricus quadrilineatus, Hartig. Cynips quadrilineatus, Thorns.
Andrims flavicornis, A. pedunculi, A. ambiguus, A. verrucosus,
A. glabriusculus, Schenck. The specific name quadrilmeatus was
given to it when it belonged to the genus Andricus, and hence it
occurs frequently as Aphilotrix qitadrilimatus, instead of quadri-
lineata. ]

92 Observations on Cynipidae.

instances does not develop into the imago for two
years ; and should the galls not be kept as nearly as
possible in their natural condition they come to nothing.
After the galls are collected t^ey must be laid on damp
sand until they become brown which is a sign that the
larva is full grown ; then it is best to put them in
a sheltered place in the open- air to pass the winter ;
if these precautions be observed we may reckon with
certainty on obtaining the flies in April.

Fly, Size 2-3 mm. long ; brownish red ; antennae
dark ; mesothorax marked by four black lines ; this
sign is very variable, as the two central lines are often
merged into each other, although in very pale specimens
they are generally plainly distinguishable. Thorax
smooth and shining, pleurae somewhat hairy, scutellum
rugose ; abdomen dark brown above ; coxae and base
of fernora dark, as well as the outer margin of the
tibiae ; rest of the legs brownish yellow. This species
has until now been very variously described ; owing to
great diversity in the colouring of the fly and in the
form of the gall, a large number of varieties have been
distinguished, all however belonging to the same
species. The most striking thing is that its first
describer, Hartig, placed it in the genus Andricus
because he believed he had found the male. How this
error arose I do not know, because it is quite certain
that males do not occur, and no entomologist has seen
them since. The flies reared from these galls are
without exception females.

Experimental breeding with this species is difficult,
because the fly is in the habit of pricking the buds

Aphilotrix albopundata. 93

of the male catkins only. The galls are however
occasionally found on the leaves, and I thought that
I might be successful in getting the fly to produce leaf-
galls, but as yet I have only been able to make one
experiment, and that gave no result. If it should be
proved that Aphilotrix quadrilineata can produce its galls
as well on leaves as on flowering catkins, this species
ought certainly to be united with Aphilotrix marginalis.
I have repeatedly watched the fly in the open air
pricking the flower buds, and I saw it do so on April
13, 1878. The fly is in the habit of concealing itself
as much as possible in the daytime, and pricks the
buds towards evening. I marked several buds which
were pricked before my eyes, and in May I could
affirm that Aphilotrix quadrilineata galls had been
formed, on catkins growing from all these buds.

[The furrowed catkin gall is found in May on Quercus sessilijlora.
Inquiline. Synergus facialis.

Parasites. Torymus auratus and Olinx trilineata. The gall is
very various in form, as the large number of synonyms indicates.]

23. Aphilotrix albopunctata. Schltdl.^
Gall. A very dainty bud-gall, like a miniature
acorn ; 4-5 mm. long ; of a greenish yellow or brownish
colour, with pale spots ; the apex distinctly umbilicate.
The gall appears in the buds in the beginning of May,
becomes rapidly mature, and falls to the ground at the
end of May. (Fig. 23.)

Rearing the Fly is easy and it emerges in the

p Cynips majalis, Giraud. Cynips albopunctata, Schltdl. Andriais
albopunciatus, Mayr. Cameron considers the fly the same as A
quadrilineata.]

94 Observations on Cynipidae.

following April, but in this species also a certain
number of flies do not emerge until the second year.

Fly. Size 3-4 mm. long ; yellowish brown ; antennae
black except the basal joint which is yellow below ;
head and thorax yellow; on the metathorax four
black lines, either distinct and narrow, or broad, in
the latter case the two central ones blending with each
other ; thorax smooth, hairy at the sides ; scutellum
rough ; abdomen yellow, black above ; legs orange ;
base of the coxae dark. This fly is very like Aphilotrix
callidoma, but it is distinguished from it by the pale
scape of the antennae.

Experimental breeding, I observed this fly for
the first time pricking a bud in April, 1875. I made an
experiment with several flies in 1876 on an oak sapling,
but I obtained no galls although some buds were pricked.
In a fresh attempt which I made on April 14, 1877,
I placed ten flies on a little oak ; they pricked several
buds, and I succeeded in getting galls. On May 10,
the first gall appeared on a bud, four more followed,
and I obtained in all five Aphilotrix albopundata galls,
so that there could be no longer any doubt that
Aphilotrix albopundata produces the same gall as that
from which it emerges.

[The spotted bud gall appears in May on Quercus pedunculata,
Q. sessihflora, and Q. pubescens.

Inquilines. Synergus facialis, S. radiaius.
Parasite. Toryyiius rnbricipes.~\

In the preceding pages I have sketched the life-
history and manner of propagation of a number of oak

Cynipidae with alternate generations. 95

gall-flies, based on observations extending over many
years. The species described belong to the fauna of
this locality (Schleswig\ but at the same time they give
a tolerably accurate illustration of the oak gall-flies
occurring in the whole of North Germany. I have
not as yet been able to make any experiments on
the South German species, nor on those occurring
only on Quercus cerris. There still remains a wide
field for observation and discovery.

In order to facilitate reference, I have arranged in
a tabular form those species of which the alternate
generation is known to exist ; and I have placed in
a separate table those which are found in one form only.

/. Cynipidae with alternate generations.

No.

Parthenogenetic Genera-
tion.

Flies
Emerge.

Sexual Generation.

Flies
Emerge.

Neuroterus lenticularis

„ laeviusctihis

„ nuntismatis

„ ftimipennis

Aphilotrix radicis . .
,, Sieboldi . .

„ corticis . .

„ globuli . .

„ collar is . .

„ fecundatrix

„ callidoma .

„ Malpighii .

,, autumtialis

Dryophanta scutellaris .
„ longiveniris

„ dt'visa . .

Biorhiza aptera . . .
„ renutn . . .

Neuroterus ostreus . .

April
( March
\ April

April

May
( April
( May
( April
1 Majr
( April
( May

April

April
April
April
April
April

(Ja.,.
I Feb.

Nov.

(Oct.
) Nov.
J Dec.
1 Jan.
J Dec.
1 Jan.
( Nov.
( March

Spathegaster baccarum

,, albipes

„ vesicatrix

,, tricolor .

Andricus noduli . . .
,, testaceipes

„ ^emmatus .

iitflator

curvator
pilosiis .
cirratus
nudus .
ramuli .

Spathegaster Taschenbergi
„ si mi lis

„ verrucosus

Teras terminalis . . .

Trigonaspis crustalis .

Spathegaster aprilinus

June

June

June
July

August

August

fjuly
I August
j June
Ijuly

June

June

June

June
uly
I May
1 June
( May
I June
I May
1 June

July

( May
1 June
( May
i June

96

Observations on Cynipidae.

II. Cynipidae without alternate generations.

No.

Exclusively Partheno-
genetic Species.

Emerge.

20.
21.
22.

23-

[24.

Aphiloirix seminationis
„ margijtalis
„ quadrili7ieata
,, albopunctata^

Cynips Kollari

April
April
April
April

( Sept.

iMay]

CHAPTER III.

On the Formation of Galls by Gall-Flies.

In the description of the oak gall-flies given in the
last chapter, the importance of an accurate examination
of the gall is repeatedly enforced. The study of the
flies must begin with the galls, they give in all cases
the best, and often the only, means of distinguishing
closely related species ; and lastly they play a most
important part in the economy of each species, because
they serve as the abode of the individual, as larva
and imago, for the greater portion of its life. I will
therefore endeavour to give a general idea of the
formation of galls.

In spite of great differences in form, manner of
formation, size, and appearance, galls can all be
referred to a common origin ; whether they grow
from the bud, leaves, bark, or roots, the parent
tissue from which they spring has always the same
physiological character. This invariably belongs to
that zone of formative cells which is called the
cambium-ring ; a layer which, beginning from the
finest root fibres, and extending to the most distant
leaves, wraps the entire plant in a tight-fitting garment.
The whole vegetable life proceeds from the cells of the

98 On the Formation of

cambium-ring. These cells are the theatre of actual
metabolism ; they are not yet differentiated into a stable
tissue, but await a period of developmental activity.
A tissue that possesses these properties possesses
the conditions essential for gall formation. When
a gall-fly has inserted its egg into the neighbourhood
of this tissue, what follows? In the first place the
act of ovipositing of itself has no effect. The wound
to the plant-tissue inflicted by a simple prick does
not necessarily give the impetus to gall formation.
Hitherto it has constantly been stated that the prick
of the gall-fly and the simultaneous introduction of
a glandular secretion excited a specific cell-growth
which led to the formation of the gall. This suppo-
sition derived a certain amount of probability from
the frequent occurrences in plants of increased cell
formation around wounds, as seen in those swellings
of the bark that follow a saw cut. Judging by
analogous phenomena occurring in animal tissues, it
was thought that the cells reacted to the stimulus of
traumatic irritation, so that increased metabolism and
the production of new cells took place. This was
made the foundation of a most misleading hypothesis ;
it was assumed that gall-flies, by means of a poisonous
glandular secretion which they poured into the wound
at the time of ovipositing, instituted a specific form of
cell activity, and in this way each species produced
its own peculiarly formed and equipped gall ; hence
it was only required to ascribe to each individual
species the possession of a specific secretion. This
view of gall formation has been supported in recent

Galls by Gall-Flies. 99

times by Lubbock \ among others ; but as early as
1873 Professor Thomas, of Ohrdruff, objected to this
explanation of it, and after numerous experiments,
I am convinced that the simple prick of the gall-fly
does not set up gall formation ; this, I hold, only begins
when the larva emerges from the egg.

But it is to be observed that in stating this view
I limit it to oak gall-flies ; there do exist gall-producing
flies in another class of hymenoptera, which produce
their galls in the way just mentioned. I have carefully
observed this in Nematus Vallisnierii. This fly, which
is armed with a finely serrated terebra, cuts into the
tender leaves of the end shoot of the Salix amygdalina,
and inserts her egg into the open wound, frequently
placing several in the same leaf. At the same time
some glandular secretion flows into the wounded leaf.
A few hours after this injury the leaf surface presents
an altered appearance, and new cell formation begins
freely, leading to a thickening of the surrounding
leaf surface. After the lapse of about fourteen days
the green and red bean-shaped gall is fully grown. If
it be now opened the egg can still be seen lying
within the cavity. The embryonic development is yet
unfinished, and three weeks elapse before the larva
emerges from the &^^, to find around it the material
prepared for its nutriment. In this case the wound
caused by the fly is the immediate exciting cause of
cell activity, and leads to gall formation. In the case
of Cectdomyidae, belonging to another division of gall-

' Sir J. Lubbock. Origin and Metamorphosis of Insects, p. 8,
1876.

H 2

loo On the Formation of

producing insects, there can be no question of any
wound of the plant cells producing the gall, because
these minute flies have no piercing apparatus. They
are enabled to introduce their egg into an opening bud
by means of a long protruded ovipositor, and then
it is the emerging larva which first stimulates gall
formation. Among gall-flies the same thing takes
place, the emerging larva invariably determines gall
production, and this can easily be proved. In the
course of the experiments in breeding, it was invariably
observed that, whether the flies laid their eggs in buds
or leaves, the wound was not immediately succeeded
by reflex plant growth. If buds in which eggs had been
laid were opened, no change was found in the interior
of the bud until the larva emerged (except of course
the delicate canals pierced by the ovipositor). It is
simpler still to observe leaf-pricking gall-flies. If a leaf
has been pricked by Spathegasler baccarum, the spot
where the ovipositor penetrated is quite visible; but
during the first fourteen days there is no further
change in the leaf surface, and this only begins on
the emergence of the larva. Undoubtedly at the time
of pricking some secretion from the poison gland
reaches the wound, but this merely serves to seal over
the cut made by the ovipositor in the leaf surface, and
does not stimulate cell activity. This is seen still
more strikingly in Trigonaspis crustalis. This fly
pricks the leaf in May, but months pass before any
trace of gall formation can be seen. It has a tolerably
strong ovipositor with which it cuts into the veins of
the leaf, and in this way a distinct mark is left wherever

Galls by Gall- Flies. loi

an egg has been inserted. Guided by these marks, it
is easy to find the eggs, but it is not until September
that the larva leaves the eg^, and then gall formation
begins.

It would naturally be interesting to observe the
exact time when the larva quits the egg and starts gall
formation ; but this is very difficult to do. Whether
the egg be enclosed within a bud or a leaf, it is
withdrawn from observation, and it is difficult to hit
off the exact time when the larva is in the act of
bursting the egg. I have several times however been
successful in observing this stage in Neuroteriis
laeviusculus and Biorhiza aptera. The moment the
larva has broken through the egg covering, and has,
for the first time, wounded the surrounding cells with
its delicate mandibles, a rapid cell-growth begins. This
goes on so quickly, that, while the posterior part of the
larva is still within the egg-covering, a wall-like growth
of cells has already arisen in front. This rapid cell
increase can easily be explained, because the irritation
set up by the emerging larva is exerted upon highly
formative cells, which collectively possess every con-
dition for growth. The cells which are primarily
around the larva cannot be distinguished from the
parenchymatous cells from which they proceed.

In every gall formation this holds good, and it will be
found that the first effect is only an increase of cell
formation in the part. A gall is not to be considered
as a parasitic growth in the surrounding tissue, but as
consisting of the same elements as that tissue, and as
substituting itself for them. Therefore the growth of

102 On the Formation of

the gall usually proceeds proportionately to the growth
of the cellular layer in which the egg is laid. Let us
take the simplest case, that of an egg laid in a leaf.
The gall formation begins in the layer of formative
cells on the under surface of the leaf, the layers of the
upper surface of the leaf are formed of cells which have
become stable ; they undergo no further change, nor
do they respond to any irritation applied to them.
They are incapable of forming new cells ; any new
formation can only originate in the cells of the under
surface. At first the gall formation only affects the
small zone of cells that surrounds it, but as soon as it
acquires a new vascular system of its own it begins to
grow apace as an independent structure.

Matters are different when the eggs are laid in the
bud, and the emerging larva comes in contact with one
of the rudimentary leaves. These consist still of
unmodified cells, which are all equally capable of
development, whether they occur on the upper or under
surface of the leaf; both surfaces consequently take
part in gall formation, and when the leaf comes to
be unfolded it is found that there is an actual absence
of leaf tissue, and that the resulting gall grows through
the leaf substance.

It is different again when the egg is laid in the
cambium-ring of the bark. Here the cells which first
form round the larva cannot be distinguished from the
adjacent cells of the cambium tissue, but in the later
cell-growth there is a sharp zonal contrast. The
peripheral zone of the cambium-ring produces the cells
of the bast parenchyma, while the central zone of the

Galls by Gall-Flies. 103

cambium produces the wood parenchyma ; and in these
galls we have similarly a soft peripheral zone of sappy
parenchymatous cells, and a hard central zone of wood
parenchyma : and in all bark galls this woody base
penetrates more or less deeply into the ligneous tissue
of the tree, while the soft fleshy periphery always
projects from the bark.

The new cell-growth is arranged in regular concentric
layers around the larva, and is accompanied by certain
changes in the cell-contents ; those cells lying next the
larva swell, the cell-contents become cloudy, and exhibit
a multitude of starch granules.

The rudimentary gall draws its first nourishment
from the surrounding tissues ; later it acquires greater
independence, for a new element comes to assist in
its further development. From the spiral vessels lying
in the cambium-ring processes are driven into the
rudimentary gall ; and the entrance of these vessels
always occurs at a definite spot on the lower surface
of the gall, whether the connexion with the parent
tissue be by a broad base or by a small stalk.

The gall has now become an independent structure,
and is practically withdrawn from the direct influence
of the cellular area which surrounds it, and from which
it sprang.

Its individuality of organization is now displayed
by most complicated transmutations of cells originally
morphologically alike. This is especially seen in the
peripheral cells, which, by assuming peculiar pigments
or by developing hairs of various kinds, exhibit an
enormous variety of forms. It is still a moot point

104 On the Formation of

in what way that differentiation proceeds which gives
to each gall its characteristic form, and regulates its
position and season.

It is the value of these different structures, as pro-
tective contrivances, which has secured their evolution
by the gall.

Pubescence, in particular, assumes an endless variety
of forms ; it may appear as a delicate down or as a thick
felt: sometimes the hairs exude a sticky sap which
deters parasites from approaching the gall ; and even
smooth galls like Aphilotrix Sicholdi secrete a juice
which, as already mentioned, serves to attract ants.
These protect them like sentinels, driving other insects
off, and often constructing a protective mantle of earth
around the galls.

The influence of the larva enters as a necessary
factor into the normal course of gall formation. If
the larva perishes before the gall is formed, it is well
known that a stunting of the gall takes place. It has
been already mentioned in the description of Aphilotrix
fecundatrix that when a roundish, undeveloped, inner
gall is found, parasites are always present ; it happens
in the same way that when an Aphilotrix collaris gall
is pricked by parasites, it grows in an anomalous
manner, and becomes consolidated with the base of
the bud. In the galls of Aphilotrix Sieboldi we often
find a similar alteration ; for if the gall is pricked by
a parasite in the course of its development, it remains
small, scarcely projects above the bark, is not regularly
striped in the normal manner, and has altogether an
appearance so different that it was formerly mistaken for

Galls by Gall-Flies. 105

a new species. At any rate this much is certain, that
the influence of the larva is necessary, not only for
the early stage of gall formation, but for the completion
of its later development. The first cells are arranged
in a circle around the larva, and mark it out as the
central point which is to dominate their growth in the
future.

A circumstance which might lead to serious error
ought to be mentioned here. A gall-fly occasionally
selects a spot where the formation of an earlier gall
has already begun, and on this spot arises its future
gall. In one case I was able to observe this satis-
factorily. The gall of Aphilotrix fecimdatrix, which is
produced by the little Andricus pilosus, is formed at
the end of June or beginning of July. At first it is
only recognizable by an enlargement or expansion of
the bud ; but about this time Andricus curvator
emerges, which also lays its eggs in buds. Owing
to the prevalence of the Aphilotrix fecundatrix galls it
not infrequently happens that Andricus curvator lays
an egg in the same bud, probably because the ovi-
positor can penetrate more easily into a swollen bud
of this kind. Later we find at the base of the mature
Aphilotrix fecundatrix gall, and between the bud scales,
the Aphilotrix collaris gall, which is produced by
Andricus curvator. I have often found two or three
Aphilotrix collaris galls in one Aphilotrix fecundatrix
gall. As the Aphilotrix collaris galls are easily over-
looked by reason of their minute size, it is obvious
that in breeding a doubt might arise as to the origin
of the flies. This peculiarity of Andricus curvator

io6 Ojt the Formation of

making use of the rudimentary Aphilotrix fecundatrix
galls is also of interest, because it is undoubtedly by
a further development of this habit that the inquilines
or lodgers have branched off from the Cynipidae, to
which they are so nearly related. The countless
inquilines of the oak gall-flies, which regularly take
possession of the great majority of galls, are the worst
enemies we have to contend with in our observations.
In their whole organization they are so nearly related
to the true gall-flies that they can only be distinguished
from them by the most minute characteristics, and
undoubtedly they have been developed from them.
By the use of a gall already formed, the prosperity of
their progeny is much more certainly insured ; un-
fortunately, however, inquilines are thus much more
easily reared and collected than the true gall-maker.

It is evident from the descriptions of individual galls
already given, that they can be produced on all parts
of the oak — on leaves, flowers, trunk, root, and buds.
In each of these organs the gall-fly finds the same
formative zone which only needs the insertion of an
egg, and escape from it of a larva, to excite gall
formation. We know also that the gall-fly proceeds
with judgement in selecting sometimes the tender
leaves, sometimes the terminal buds, and sometimes
the flower buds for its particular purpose. In spite,
however, of every care numerous galls fail, as we have
already noted, even where there can be no doubt that
the eggs had been laid by the fly.

What causes this frequent failure of the galls ? We
might at first imagine that there had been some inter-

Galls by Gall- Flies. 107

ferencewith embryonic development, but I must confess
that I have seldom found a dead egg which had not
reached development. The cause lies elsewhere. It
was constantly remarked that, in the different culture
experiments made, the greater proportion of the galls
failed. This was most easily observed in the case of
flies that produced bud-galls, and which, therefore, lay
only one egg in the bud. Naturally the species
emerging in summer can only prick winter buds which
are awaiting the next period of vegetative activity. In
this circumstance we may discover one reason for the
failure of the galls, for we may assume that, in many
seasons, a premature and anomalous development of
winter buds may be absent. But, according to all
observations, this cannot be the only reason ; indeed,
the first essential to insuring gall growth is the
right position of the egg. Gall formation will not fail
if the larva, when it emerges from the Q:gg, meets with
its appropriate cell surroundings ; but to secure this
the fly must lay its egg with the greatest exactitude.
In the case of winter buds, it is especially important
that the egg be placed exactly in the zone of the
cambium-ring, which lies like a fine seam in the
base of the bud. We see that from the winter buds,
without exception, only bud-galls, and not leaf-galls,
are produced ; a proof that the larva has no power to
unfold the leaf-germs, but that gall formation can only
proceed from the zone of the cambium-ring ; and if
the egg should not have been laid by the fly exactly
where the emerging larva could reach this fine zone,
it perishes without forming a gall. If we think of the

io8 On the Formation of

great natural difficulties the fly has to overcome in
laying the egg with this degree of accuracy, it is not
surprising if many eggs come to lie amiss. It is not
possible to believe that the emerging larva can alter its
position in any way, because it has not the means of
locomotion; and, besides, the egg is so closely sur-
rounded by the tissues of the bud that any movement of
the larva is rendered impossible.

I certainly believe that failures are most common in
those cases where buds are pricked, and where the
emerging larva produces a bud-gall ; they occur much
less frequently in those species which produce leaf-
galls, because in these the fly can utilize a much
wider territory, extending over the whole of the rudi-
mentary leaves in the bud. But even then it certainly
does sometimes occur that eggs are not within reach
of the rudimentary leaves, and unavoidably fail. Another
confirmation of the view that malposition of the egg is
the chief reason for failure of gall formation, is found in
the fact that failures are not usually observed in those
cases where the fly cannot easily miss the cambium-zone.
This is well seen in those species that prick the bark
and the surface of the leaf; in these, only the outer
layer of epidermis requires to be pierced, and the cell
region sought for is always situated about one uniform
depth ; while in the case of buds of indefinite size and
shape, the form of the bud axis, sometimes longer,
sometimes shorter, gives a varying measure for the depth
to which the ^%^ must be sunk.

The development of the gall is closely dependent
upon the vegetative periods of the oak, and ceases with

Galls by Gall-Flies. icg

the close of those periods ; on this account we see that
most galls mature in the space of a year. There are
some species certainly which require two years, these
are always bark-galls ; in the first year the rudiment
only of the gall is formed, and its further development
is arrested until the next spring, when gall formation is
renewed with a fresh period of vegetative activity.

CHAPTER IV.

The Piercing Apparatus. — The Method of Ovipositing. — The
Object and Function of the Egg-stalk.

Gall formation, as we have seen, is a complicated
process, and necessitates the possession of a very
elaborate apparatus to ensure the deposition of each
egg in exactly the right spot for gall growth. We
consequently find that the gall-fly is furnished with
a peculiarly constructed piercing apparatus, of which
it is necessary that a short description should now
be given.

The terebra itself consists of three pieces, for the
nomenclature of which we, in Germany, follow Krae-
pelin ^ ; they are a ridged seta ^ and two serrated
spiculae ^. The two spiculae are similar to each other,
and the seta is also clearly derived from two symmetrical
halves united into one piece. The seta occupies half
the area of a tranverse section of the terebra, and the
two spiculae together occupy the other half. The
terebra is attached to two peculiarly formed chitinous
plates which in repose are quite concealed within the

^ Kraepelin, ' Zeitschrift fur wissenschaftliche Zoologie,' vol. xxiii.
Part II. 1872.
^ Schienenrinne. ' Stechborsten.

The Piercing Apparatus. iii

abdomen. These plates may be distinguished as the
anterior (outer) and posterior (inner) plate, a description
which is perfectly clear when the ovipositor is placed as
it lies in the abdomen of the fly. The accompanying
illustrations (Plate III) exhibit the ovipositor always in
this position. An examination of the drawings will
show that these chitinous plates are found in a great
variety of forms, and this variation gives to each
species its characteristic formation of ovipositor ; but
the connexion between them and the terebra is always
the same, and the groups of muscles are alike in every
ovipositor.

Their connexion with the terebra is as follows — at
the origin of each spicula is a broad and almost
triangular plate, the angular plate ^ of Kraepelin, which
is articulated with the anterior and posterior plates by
hinge-joints, but the articulation with the posterior
plate is freer and more moveable than with the
anterior. This double articulation of the two spiculae
has the obvious advantage of enabling them to be
thrust to and fro, while they are at the same time
securely maintained in position.

There are certain groups of muscles which set the
spiculae in motion, but these act primarily through the
two plates to which they are articulated. Each muscular
contraction causes a movement of the plates which is
transmitted to the triangular plate, and thence the motion
is communicated to the spiculae by their connexion with
the triangular plate. A to and fro movement of the
spiculae is thus the only possible one, and at the same
1 Winkel.

iia The Piercing Apparatus.

time it is the only movement necessary in the act of
ovipositing. Nevertheless, many muscles are required
to accomplish this movement.

We pass to the examination of the other portion
of the terebra, the seta. The seta is only connected
with the two anterior plates, and like the whole ovi-
positing apparatus, it is throughout composed of two
symmetrical halves. From the upper rim of each
anterior plate springs what is called the arch, which
passes directly into, and is the origin of the seta. The
point where the two arches amalgamate is the origin
of the seta. On its lower surface, at this point, the seta
bears a well marked chitinous projection, called the
horn, which is important, because it forms the insertion ,
of a strong muscle. In consequence of its origin and
the way in which it is strengthened, the seta possesses
only a moderate degree of mobility.

The chitinous framework of the terebra may be seen
when it is removed from the body, and it also comes
partly into view during ovipositing ; but further pre-
paration is necessary in order to see and understand
the action of these muscles. To expose them, the two
pairs of plates, which are firmly united and enclosed
in a chitinous membrane, must be separated in the
middle line, when the muscles belonging to each pair
of plates will be found placed on their inner surface.
In all, we have five pairs of muscles to examine.

Beginning with the anterior plate, we see that the
first muscle, a very powerful one, takes its origin from
the upper third of the plate, and spreading like a many-
rayed fan is inserted by a strong tendon into the root

The Piercing Apparatus. 113

of the seta (called by Kraepelin the horn). By its con-
traction this muscle draws upon the horn, and thus
raises the seta from the position it occupies in repose,
and directs it downwards : this is the first introductory
movement in ovipositing.

The second, a smaller muscle, also takes its origin
from the anterior plate, chiefly from the arch, and is
inserted by a long chitinous tendon into the base of the
horn near the last muscle. The contraction of this
muscle draws the seta towards the anterior plate, and
it is thus the antagonist of the former one. This
muscle also varies greatly in strength, being sometimes
reduced to a few fibrillae ; in Neuroterus laeviusciiliis it
is entirely wanting, and the first muscle is also very
feebly developed in this fly.

The third, a powerful muscle, arises from the hamu-
lar process of the anterior plate and from the margin
of the notch in which the angular plate lies ; it is
inserted, by a long line of attachment, into a strong
chitinous ridge on the posterior plate. The contraction
of this muscle draws the posterior plate upwards. This
movement is communicated to the angular plate, and to
the spiculae connected with it, and the result is that
these latter are thrust forward. This movement is of
the greatest importance, for it is by the spiculae, when
thus thrust forward, that the first opening is made,
through which the whole ovipositor is pushed into the
tissues of the plant.

AfourtJi very powerful muscle springs from the pro-
jecting rim of the anterior plate and is inserted into the
upper half of the posterior plate. By the contraction

I

114 The Piercing Apparatus.

of this muscle, the posterior plate is drawn towards the
anterior one, and thus the protruded spiculae are again
withdrawn. In this way this muscle is the antagonist
of the last one.

A fifth muscle springs from the margin of the notch in
the anterior plate, near the third muscle, the action
of which it supplements.

Owing to their concealed position, it is not possible
to observe how these muscles act in the living fly, but
the movements of the insect as they occur in egg-laying
can nevertheless be seen. They may be watched very
plainly in Ncuroterns laeviuscidus. The long ovipositor
of this fly (PI. Ill, Fig. 2) hidden in the abdomen during
repose, comes perfectly into view while ovipositing, and
the two pairs of plates are seen at the same time.
But as the exact movements of the spiculae are only
observable during the slight protrusion of the plates, it
is necessary that we should have the plates exposed in
order to observe the character of these movements
properly. This may be demonstrated in the following
way. Wait until the Neuroterus laeviuscuhts pricks the
bud, and when the ovipositor has penetrated into the
bud, try by a quick movement to pull the fly off; the
ovipositor is too firmly fixed, resists, and breaks off \
There remains connected with it the whole motor
apparatus, and also the large ganglion which innervates
the muscles ; consequently the pricking movements
proceed regularly until the muscles die. It is then

[' Lichtenstein states that this often takes place when the flies are
at liberty, and in spring he had frequently found the ovipositor and
part of the abdomen of a cynips fixed in a bud.]

Pla-te ni

OaM-'Jcli. J'lic.

Tr.v/=*.-, hth.

The Method of Ovipositing, 115

quite evident that the anterior plate remains always a
fixed point, while on the contrary the posterior plate
is drawn alternately up and down. By these simple
movements of the posterior plate, the insertion and
withdrawal of the spiculae are carried on ; the thrusting
out of the spiculae is the harder operation, and is
effected by two powerful muscles ; while their with-
drawal is easier, and requires only one muscle. The
anterior plate remains passive during the act of ovi-
positing, therefore the seta, which is firmly united
to it, takes a less active part ; it is pushed steadily
forward by the fly and is driven into the canal that has
been bored and opened by the spiculae.

We must next inquire into the manner in which the
gall-fly introduces the egg into the bud by means of
this apparatus. Hartig's explanation, which has hitherto
been received, was that the extremely ductile egg was
driven through the ovipositor itself. He thought
that the contents of the egg passed into the egg-stalk
and were collected in its club end, but after the real
egg-body had been thrust into the plant tissue, the
contents streamed back again into it. Hartig thought
this theory all the more probable, because the passage
of the yolk into the egg- stalk could actually be observed
in the eggs of the Cynipidae. This is easily seen under
the microscope if the egg, taken from the ovary, be
examined in water. We shall refer later to the mean-
ing of this phenomenon, when we come to compare the
length of the egg-stalk with that of the ovipositor, but
Hartig's theory must be abandoned as unsatisfactory.

In every case^the ovipositor is considerably longer
I 2

1 1 6 The Method of Ovipositing.

than the egg, as may be seen by referring to the
diagrams in Plate III, where the eggs and ovipositors
are all taken from photographs, and are drawn of the
same amplification. It follows therefore that one end
of the egg cannot be sunk in the plant tissue while the
other is still in the canal, and the explanation of Hartig
consequently fails.

Besides, it is not possible that the whole egg could
be received into the ovipositor and could glide through
it, for the ovipositor cannot be compared to a hollow
tube. It consists, as already stated, of three parts which
are firmly connected with each other. The upper is the
ridged seta, on the under surface of which the two spiculae
are mortised by two tenons. The seta certainly en-
closes a central cavity, but it has no connexion with the
canal, and merely serves to contain a nerve branch, an
air vessel, and some sanguineous fluid. Therefore the
egg cannot pass through the ovipositor in the way
Hartig supposed. On the other hand, there is sufficient
space between the two spiculae to admit the egg-stalk.

It is still difficult to understand how the egg is finally
protruded into the bud. We can clearly recognize the
movements of the ovipositor made by the fly, but we are
unable to follow the movements of the egg, and only in
one way do we get any knowledge of this part of the
operation. Nenroterus laeviusculus requires from fifteen
to twenty minutes for the act of ovipositing. If a prick-
ing fly were fixed in position, by being suddenly dipped
into chloroform or ether, and the bud were opened, we
could then see how far the ovipositor had penetrated,
and whereabout the egg was : and if, during the fifteen

The Method of Ovipositing. 117

or twenty minutes occupied by the laying of the ^%^,
a pricking fly could be fixed in position every successive
minute, the buds would yield us a long series of pre-
parations exhibiting the different stages in the birth of
an egg. Unfortunately this idea cannot be carried
out, on account of practical difficulties. In the first
place the time occupied in pricking the buds is not
always the same, and in the next each separate act is
itself of uncertain duration, since the fly has greater
obstacles to overcome in some cases than in others.
It is therefore only possible to learn to recognize some
of its different stages, and then from these to construct
the whole operation.

We shall begin with the moment when the fly
places its ovipositor on the bud. She always chooses
the edge of one of the outer scales as a point of attack,
and pushes her ovipositor under it. Then the ovipo-
sitor glides under the scales to the base of the bud-axis.
Even this first act requires great strength on the
part of the fly. We sometimes see it attack the bud
repeatedly with its ovipositor, before it succeeds in
getting it under the scales. It does not succeed with
buds in which the scales are closely imbricated, hence
it always prefers buds with loose-lying scales. When
the ovipositor has arrived at the base, it is driven
towards the bud-axis so as to reach the rudimentary
leaves ; but the path made by the ovipositor is always
more or less curved. By making a careful prepara-
tion of any pricked bud, the canal can be plainly seen,
and the path taken by the ovipositor followed. After
the fly has finished the first part of its work, and

1 1 8 The Method of Ovipositing.

driven the ovipositor into the centre of the bud, there
comes a moment of complete rest, and the fly sits
motionless upon the bud. If it is fixed in this position
by dipping it into chloroform, nothing is seen of the egg,
it still remains in the vagina. Then follows the second
part of the work, the pushing of the egg into the bud.

The egg slips, with its enclosed egg-body, to the base
of the ovipositor between the origin of the two spiculae.
The egg-body glides over the point where the two
spiculae embrace the tenon of the seta, since the space
remaining open between the two spiculae is too small
to admit it. But the egg-stalk, which follows, slips
between the two spiculae, is seized by them, and
driven forward ; in this way the ^%% is pushed
downwards into the ovipositor, with the egg-body
hanging out.

When at last the egg is about to enter the canal
which has been bored into the centre of the bud, it
becomes evident that it is impossible for the canal to
admit the ovipositor and the egg-body to pass in at the
same time. The egg-body is always of much greater
diameter than the ovipositor ; on this account the ovi-
positor is next partially withdrawn by the fly, until the
pierced canal becomes empty ; the egg-body then enters
the pierced canal, and the ovipositor follows, pushing it
before it. In short, the whole forward motion is
dependent on the egg-stalk being propelled by the to
and fro movements of the two spiculae, and the &^'g
reaches the end of the bored canal, while the egg-stalk
remains lying within it.

The process of egg-laying, though it seems rather com-

77?^ Method of Ovipositing. 119

plicated, can be divided into three stages, (i) The canal
is bored, the ovipositor gliding under the imbricated
scales to the base of the bud, and then being driven into
the centre of the bud-axis. (2) The e^^ passes out of
the ovarium to the base of the ovipositor, where the egg-
stalk is pinched between the two spiculae, and the egg
is pushed along the ovipositor. (3) After the point of
the ovipositor is withdrawn, the egg-body enters the
pierced canal, and is pushed forward by the ovipositor
until it reaches the bottom.

If we consider all this varied procedure, we cannot
but be astonished at the accuracy with which the fly
carries it out, and repeats it many times in succession.
Only one egg can ever pass through the same canal ;
there is no room for a second, because the egg-stalk of
the first egg remains 13'ing in the canal.

Those flies which lay their eggs in leaf surfaces have
naturally a much easier task, since they have only to
pierce a thin membrane. The mechanism of ovipositing
however is exactly the same.

We shall next consider a provision existing in the
terebra, by which the fly is enabled to carry out all the
operations required in ovipositing, with the greatest
exactitude. For this purpose its rigid chitinous armour
is furnished with tactile hairs at various points. The
tactile organs peculiar to insects consist of fine hairs,
connected at their bases with ganglionic swellings of
sensory nerve-matter, and they are found at various
parts of the ovipositing apparatus. They occur con-
stantly, in all hymenoptera, on the arch of the anterior
plate. Their number varies in different species from

1 20 The Method of Ovipositing.

twenty to fifty. We must not ascribe any mechanical
function in the process of egg-laying to these delicate
hairs ; they are merely tactile organs, each hair being
in connexion with a nerve fibre. These nerve fibres
all arise from the large abdominal ganglion, which also
gives off" motor fibres to the piercing apparatus \ The
tactile hairs scattered over the arch have the important
function of informing the fly as to the true position of
the egg. While the egg is gliding over the hard
chitinous covering of the ovipositor, the fly only becomes
conscious of its progress from one stage to another,
when it touches a tactile hair ; these serve to signal its
advance. Such hairs are consequently placed more
closely on the arch, where the egg is caught between
the two spiculae ; and by their means the fly is guided
exactly to where the egg-body is to be found. When
the egg has reached the proper point, the egg-stalk is
apparently seized by a rapid to and fro movement of
the two spiculae. Thus all the time the egg is being
pushed down to the ovipositor, there is a provision for
keeping the fly informed of its progress by sensation.
There are also on the seta, particularly towards its
point, organs of sensation, not in the form of hairs but
of slight projections of the chitinous membrane. There
are besides, in some hymenoptera [Platygaster], perfect
hairs on the point of the ovipositor. The sensory
branches of the nerve, which is contained in the central

^ In no other order of insects is the abdominal gangHon so power-
fully developed as in the hymenoptera ; this is due to the fact
that it has to undertake the innervation of the complicated piercing
apparatus.

The Method of Ovipositing. 121

canal of the seta, are distributed to these organs of
touch. In consequence of this provision, the fly uses
the ovipositor as a feeler, and chooses with precision
the spot in which the egg is to be deposited. The fly
would otherwise fail to find within the bud either the
region of the rudimentary leaves, or the meristem in
which it is essential that the egg be placed, to secure
subsequent gall formation.

A further proof of the delicacy of feeling possessed
by gall-flies is shown by the fact, previously mentioned,
that many species prick flower-buds only. Here, it is
true, the fly also uses its antennae in selecting the buds.
If we observe an ApJiilotrix fecundatrix vihich. has been
brought indoors upon a detached bough, we shall see
that it is by careful feeling that she finds out the flower-
buds, to prick them. Certainly it may happen that
she lays an egg occasionally in a leaf-bud, but as if she
had found out her mistake, she immediately quits the
leaf-bud. During these experiments I tried to find out
if it was possible to distinguish between a leaf-bud and
a flower-bud, and I discovered that there were certain
appreciable differences between them. In flower-buds
the mass of rudimentary stamens gives the bud a larger
circumference than that of one which contains leaf rudi-
ments. Now in one bud all the leaf rudiments may be
supplanted by pollen rudiments, or they may occur
together. The greater the proportion of pollen rudi-
ments found in a bud, the more altered is its contour,
and the whole bud has quite a different appearance ;
it is thicker in the middle, and more slender at the apex
than other buds. I tried to guess before-hand whether

12 2 Object and FtincHon of the Egg-stalk.

certain buds were leaf-buds or flower-buds, and in most
cases my conjectures were correct. Sometimes even
after the fly has closely examined the bud with its
antennae, it may happen that the ovipositor, in piercing
it, affords different information, and immediately the
fly will leave that bud and seek another. The mere
fact that several galls occur only on the flowering
catkins, shows that the flies know how to distinguish the
flower-buds from others.

In the descriptions of oviposition which I have already
given, it has been repeatedly shown that it is by means
of the egg-stalk being seized by the two spiculae and
pushed onwards, that the egg itself is drawn out. But
this cannot be the special function and intention of the
egg-stalk, as the following facts show. In the first place
it is very remarkable that stalked eggs occur only in
a small division of the hymenoptera ; and that they are
entirely wanting in the Pimplidae and Cryptidae, which
are mostly provided with very long ovipositors. We
are justified therefore in concluding that the stalk is
not absolutely necessary for the extrusion of the egg.

The eggs of the Cynipidae are further distinguished
from the stalked eggs of other hymenoptera in this, that
in the former the egg-stalk is attached to the anterior,
in the latter to the posterior egg-pole ; consequently at
the birth of the egg in the first case, the real egg-body
takes the lead ; in the latter, the egg-stalk. This does
not agree well with the explanation given by Hartig,
who, neglecting the anatomical relations of the parts,
assumed that in the Cynipidae also, the egg-stalk was
born first. The egg contents according to this ought

Object and Function of the Egg-stalk. 123

to stream first into the egg-stalk and afterwards back
into the egg-body. But there is a point of still greater
importance — the egg-stalks of Cynipidae are not similar
in origin and formation to those of the other hymeno-
ptera. If we examine a stalked egg of Tryphon, the
stalk is very differently formed ; it appears as a solid
appendage to the egg-envelope, and is to be regarded
as a cuticular formation. It is intended to be bored
into the skin of caterpillars. The stalk of Cynipidae
eggs has a totally different intention. It is not a simple
appendage, but contains a cavity in direct connexion
with the yolk sac ; and its extremity has a club-like
dilatation. Therefore part of the yolk can enter the
egg-stalk without difficulty, and, as has already been
stated, this actually occurs each time an egg is laid.
This peculiar form of egg seen in Cynipidae can easily
be recognized within the ovarian follicles in an earlier
stage of development. In Plate III, Fig. 9, part of
the egg-tube of Neuroterus fumipennis is represented
exhibiting the origin of the egg-stalk. On the younger
egg-germ nothing is yet to be seen of the stalk, and the
yolk mass has assumed a cylindrical form ; in the
more developed egg-cell the flask-shaped form of the
yolk shows plainly the egg-stalk in course of formation.
Later the younger egg-cells, as seen in the last egg,
develop egg-stalks and come to lie finally against
the wall of the egg-tube, overlapping each other like
tiles. To appreciate exactly the intention of the egg-
stalk, it is necessary to observe a still later stage of
embryonic development, at which it sometimes occurs
that the egg-body expands and enlarges to a remarkable

124 Object and Function of the Egg-stalk.

degree. Compare (Plate III, Fig. 8) the egg of Biorhiza
aptera taken from the ovary, with another laid in
January, and taken out of the bud in the beginning of
April. What causes the striking increase in the circum-
ference ? Evidently half of the egg is filled with fluid.
The embryo lies at the posterior pole, and scarcely
occupies half the egg-chamber ; in front of it lies a sac
containing fluid, which does not enter into the egg-stalk,
but stops short at its commencement. The embryo is
surrounded by a very delicate membrane, floating, so
to speak, in this fluid. The egg-stalk takes part in the
expansion, particularly at its club-like end, and is also
filled with fluid. What can be the use of this con-
trivance? We have seen that the club-shaped end of
the egg-stalk is the last to enter into the portion of the
plant prepared to receive it, and remains close to the
surface. It is separated, as a rule, from the outside air
by a single thin bud-scale only, and consequently this
part of the egg-stalk is accessible to the ph3^sical
influences of the atmosphere, and admits of gaseous
interchange. The fluid in the club-like end, enclosed
by a very delicate membrane, can thus absorb oxygen,
and as the egg-stalk is merely an extension of the egg
cavity, oxygen can be conveyed to the embryo in this
way. Therefore, as I understand it, the egg- stalk has the
function of a respiratory organ.

In support of this theory I would adduce the following
facts. The embryo of Cynipidae eggs requires a supply
of oxygen at a very early stage of development. A long
time before it comes to perfection, it is the seat of
continual movements. The Biorhiza aptera egg (PI. Ill,

Object and Function of the Egg-stalk. 1 25

Fig. 8) contains an embryo in which the rudiments of
the head and mouth are all that can yet be distinguished
with certainty ; but even at that early period, regular
rotation takes place, by which we sometimes obtain
a side view, and sometimes a front view of the embryo.
These movements follow with a slow, wave-like succession
peculiar to sarcode, and are unlike the quick contractions
of true muscular tissue. It is possible to observe this
embryonic state six weeks before the larva attains per-
fection. Where such continuous movements are taking
place, a supply of oxygen appears to be indispensable.
The egg, however, while lying deeply in the heart of the
bud, can only obtain this supply of oxygen through the
egg-stalk, because no gaseous interchange can take place
through the thick walls of the bud. The surrounding
plant tissue which is in a state of rest, and in which no
metabolism is going on, can afford no such supply.
This, it will be seen, imparts a fresh importance to the
fact that the egg-stalks are of varying length. If the
egg-stalk had only been intended for the purpose of
dragging the egg along the ovipositor when it was
being laid, a short egg-stalk would have been sufficient.
But the lengths are very different, and I believe I can
show that they are regulated by the thickness of the
layer that separates the egg-bodies from the surrounding
atmosphere. As the egg-stalk is a continuation of the
yolk sac, and ought to remain in the closest possible
relationship with the air, we find that a long stalk is
constantly present in eggs which are deeply sunk in the
bud. As a rule, a long egg-stalk belongs to a long
ovipositor, but there are exceptions, and it is precisely

1 26 Object and Function of the Egg-stalk.

these which confirm my theory. A glance at the
illustration (PI. Ill) shows that Andricus noduli has
a very short egg-stalk with a relatively long ovipositor.
We must remember that Andricus noduli lays its egg
in August, in the cambium layer of the oak bark : but
there can be no want of oxygen in a plant tissue in
which metabolism is constantly going on, and it is not
therefore necessary to inhale oxygen by means of the
egg-stalk. The summer generations of many species
lay their eggs under the same favourable circumstances
as Andricus noduli, therefore their egg-stalks are
short. But this holds good only of species which lay
their eggs in leaves ; and we must except those which
prick the winter buds. As winter buds are properly
speaking resting buds, the surrounding plant tissues
can afford no nourishment, consequently the egg-stalk
must be long enough to come in contact with the outer
air. Against this explanation of the use of the egg-
stalk the fact may be advanced that in other hymeno-
ptera this contrivance is wanting, but it would not be
difficult to prove that in none of these cases is such
an arrangement needed. Thus all the Ichneumonidae
give over their eggs to the selected host, and in its body
they obtain all the nourishment they require. Many
saw-flies also sink their eggs into various parts of the
plant, but they do so always at a time when active
metabolism is going on. In the case of oak gall-flies on
the contrary, the eggs of most of the winter generations
are laid at a time when the plants themselves give no
signs of life, and when metabolism is dormant.
Another apparent objection is that inquilines closely

Object and Function of the Egg-stalk. 127

allied to the Cynipidae have also stalked eggs. In this
case we cannot ascribe to the stalk the important
functions of a respiratory organ, as the egg does not
need it ; but nobody can doubt that their great con-
formity in outward habit and whole organization proves
that these inquilines have been evolved from the
Cynipidae, and the peculiarity of the stalked egg has
remained with them as a survival. But in their case
the egg-stalk is not required to act in the way described,
and does not do so ; because the peculiar conditions of
embryonic development, which we find existing in
Biorhiza aptera, are wanting in them.

In order to explain the function of the egg-stalk,
I have spoken of embryonic development in its ad-
vanced stage ; but the egg-stalk plays a part also at
the moment when the egg is being laid. It has already
been explained that the egg cavity communicates with
the egg-stalk, consequently part of the contents of the
egg can pass without impediment into the stalk. This
happens regularly at the laying of each egg. If an egg
which has been laid by a fly in a bud, is afterwards
removed, the preparation will show the first part of the
egg-stalk to be quite full of a finely granular emulsion
which forms the egg contents. After a time changes
take place in this emulsion, and there are formed in it
highly refractive globules of various sizes ; finally the
whole contents of the egg-stalk clear, and a fine mem-
brane appears, separating the egg-stalk from the egg
cavity. These preparatory changes are always a sure
sign that egg development is taking its proper course ;
a matter as to which we may sometimes be in doubt

128 Object and Fimdion of the Egg-stalk.

when we remove a freshly laid egg from a bud, to be
further examined in the damp chamber. Although
I have frequently observed this occurrence in the egg-
stalk, I am unable to explain it more clearly. This
much is certain, that it is a phenomenon of great im-
portance, and it is only after it has taken place, that eggs
kept in the damp chamber are observed to undergo
the various stages of embryonic development. But
I have never succeeded, no matter how careful the
precautions adopted, or what the modifications under
which I carried out the experiment, in bringing an egg
to perfect development, after removal from the ovary
of a parthenogenetic fly.

CHAPTER V.

Comparative Classification of Corresponding Generations of
Cynipidae according to their Organization.

The activity of the fly culminates in the act of
oviposition ; care for its progeny occupies the whole
period of its individual existence. I began therefore
by giving a description of the complicated apparatus by
which egg-laying was carried out, and I now proceed
to compare the whole organization of the two genera-
tions in the various stages of imago and larva. I have
already described in detail the outward configuration
of the gall-flies, and the differences in colouring, sculp-
ture, and pubescence which they exhibit.

Outward characters are usually of little distinctive
value in gall-flies ; a uniformly dull colour prevails in
almost all species ; and there are many which cannot
be distinguished from each other by an outward examina-
tion of the flies only. In comparing two alternating
generations, colouring counts for little ; their form,
structure, and size are of much greater significance.
In these respects there are very important differences
in the two generations. If a Ncuroterus and its
corresponding Spathegastcr form be compared with

130 Comparative Classification of Cynipidae.

each other, they could never be mistaken in spite of
considerable similarity of colouring. The size may be
nearly the same, but the form of the thorax, the cut of
the wings, and the configuration of the abdomen are
so different, that it would be impossible to confound the
two insects. These outward differences are still further
confirmed by the form and structure of the ovipositor.
The delicate little ovipositor of Spaihegaster takes up
very small space, while the long spirally-coiled ovi-
positor of Neuroterus requires the whole abdominal
cavity to contain it, and hence the difference in the
contour of the abdomen. Again, the manner in which
Spathcgaster bores into the leaves requires a greater
mobility of the abdomen, and so we find it is distinctly
pedunculated ; Neuroterus on the contrary is almost
sessile. Lastly, Spathegaster selects only leaves of very
tender consistence in which to lay its eggs, and must
consequently be able to fly easily; we find Spathe-
gaster therefore provided with longer and broader
wings than Neuroterus, which can everywhere find buds
in which to lay its eggs, and needs no particular power
of flight. While in a manner we can thus construct
the whole insect from the ovipositor, it is also possible
to distinguish with certainty the various genera by its
different methods of action. If two alternating genera-
tions live in perfectly distinct outward conditions, it
is absolutely essential that the ovipositor should
accommodate itself to them, and take that form which
is most suitable for the proper insertion of the eggs.
If one generation appears at a season when there are
only buds to be found, it must be provided with an

Neuroterus-Spathegaster Group. 131

ovipositor fitted for piercing buds ; and if on the other
hand the following generation appears at a season
when both buds and leaves are found, a perfectly
different form of ovipositor will be necessary for
piercing the latter. An accurate knowledge of the
ovipositor is of importance in investigating the history
of those species of gall-flies whose alternate generation
is not yet known. For instance, if a fly is reared from
a leaf-gall, and is furnished with an ovipositor which
is not adapted for piercing leaves, it may be inferred
with certainty that another generation, capable of pro-
ducing leaf-galls, belongs to this fly.

It will be found of interest, therefore, to review the
various forms of ovipositor described.

I. Neuroterus-Spathegaster Group.

A glance at the illustrations ^ of the two ovipositors
will enable us to appreciate their great difference. In
Neuroterus laeviusculus (Fig. 2) the ovipositor is very
long and spirally coiled ; in Spathegaster albipes, on
the contrary (Fig. 2'^), it is short and slightly curved.
The other species of Neuroterus show a somewhat
shorter ovipositor, especially Neuroterus fumipennis
(Fig. 3). Spathegaster ovipositors do not vary. The
Neuroterus ovipositor has a hook-shaped point, and
can therefore never penetrate perpendicularly into a
bud. The Spathegaster ovipositor, being only slightly
curved, can pierce vertically the surface of the leaf.

^ I may here remark that the illustrations are all drawn from
photographs, and therefore give exact relative proportions. The draw-
ings of the eggs near them are also photographed on the same scale.

K 2

132 Comparative Classification of Cynipidae.

The different form of the plates in these two ovi-
positors is especially striking. In Neuroterus they are
almost circular, and owing to their great curvature, there
is no room for the usually strong muscles of the
anterior plate (Fig. i. No. i). This muscle therefore
appears quite rudimentary, and the second muscle
which springs from the arch is wholly wanting.

II. The Aphilotrix-Andricus Group.

In this group also, we meet with differences in the
ovipositor, but in some cases they are very slight. If
we compare the two ovipositors of Aphilotrix radicis
(Fig. 4), and Andriciis nodiili (Fig. 4^), a general
harmony is observed, but functional differences are
easily recognized. The radicis ovipositor ends in
a sharply curved point, and is consequently not adapted
to penetrate perpendicularly into plant tissue ; the fly
must drive it into the bud in a circuitous fashion. The
ovipositor first glides under the bud-scales to the base
of the bud-axis, and is then directed upwards. The
nodtdi ovipositor, on the contrary, can penetrate per-
pendicularly into the bark with its straight point.
But with ovipositors so much alike as these, it is well
to have some further marks of distinction. At the end
of the posterior plate, in all gall-flies, there is a little
papilla which is distinctly prominent, of slender form,
and thickly covered with tactile hairs. The corre-
sponding parts of the ovipositor, and of the two posterior
plates, lie closely on each other, but room for the
protrusion of the rectum must be left between them.
For that reason there is in each plate a little notch,

Aphilotrix-Andricus Group. 133

which is covered by this papilla, and between the two
papillae of the posterior plates, we find the aperture of
the anus. The shorter the ovipositor, the nearer to the
end of the plate is the papilla ; the longer the ovipositor,
the further up is the papilla situated ; we should
accordingly expect to find in Andricus noduli a. relatively
long ovipositor. We also know that Andricus noduli
must bore through the bark, in order to reach the
cambium-ring, therefore the ovipositor must be long
enough to penetrate a depth of 2 mm. It measures
about 2-5 mm., and is thus longer than the whole fly.

In other species of Andricus, a relatively short
ovipositor is found, and consequently the papilla is
placed nearer the end. This can be recognized in
the ovipositor of Andricus cirratus (Fig. i). It enables
the fly to bore into the winter buds while small and
scarcely developed ; and in these it is only necessary
to penetrate at the furthest 0-5 mm. in order to place
the egg in the centre of the bud-axis.

The longer the ovipositor the greater, relatively, will
be its spiral curvature ; but in order that the passage
of the rectum may suffer no infraction, it must always
occupy the same position ; therefore its aperture is
sometimes nearer, and sometimes farther from the ends
of the plates of the ovipositor. An examination of the
figures in Plate III shows that the length of the plates
and of the ovipositors are always the same, because the
small processes of the posterior plates form the sheath
of the ovipositor, and enclose it when at rest.

However similar in some cases the ovipositors of
the two generations may appear, there is a constant

134 Comparative Classification of Cynipidae.

difference ; the Aphilotrix ovipositor is always curved,
and more or less hooked at the point, because, as has
been stated, it is never bored directly into the centre
of the bud, like the Andncus ovipositor, but always in
a curved manner.

III. Dryophanta-Spathegaster Group.

In this group the two forms of ovipositor differ
markedly from each other, because the method of
piercing is quite dissimilar. Dryophanta bores into
the buds, Spathegaster into the veins of the leaf The
former is provided with a very strong ovipositor which
is only slightly curved, and particularly straight at the
point ; the latter with a short one, somewhat hooked
at the point. Dryophanta behaves differently from
those flies, previously described, which pierce buds : it
applies its ovipositor perpendicularly to the bud, and
bores straight down into it ; the egg thus comes to lie
in the centre of the bud-axis, or on one of the
rudimentary leaves. Spathegaster only pierces the
epidermis of the leafveins, and pushes the egg into
the opening it has made.

IV. Biorhiza Group.

In this group we have considered two species, Biorhiza
aptera, and Biorhiza renum, which can scarcely be united
in the same genus. This is very evident when we
compare the two sexual generations with each other.
Biorhiza aptera resembles the sexual generation Teras
terminalis so closely, that any well marked points of

Biorhiza Group. 135

difference can hardly be found ; even the ovipositors
have the same form. Although the two flies do not
pierce the same parts of the plant {Biorhiza aptera
pricks buds almost entirely, and Teras terminalts only
the bark), yet the form of the ovipositor is alike, because
the parts of the plant they severally attack are pierced
perpendicularly. Biorhiza renunt has a differently
formed ovipositor from Biorhiza optera, although it is
also intended for piercing buds. On the contrary, Trigon-
aspis crustalis, the sexual generation, has a quite
differently shaped ovipositor, which agrees with that
oi Spathegaster Taschenbergi, and like it is destined to
pierce leaf-veins. It is evident that variety of form
in the ovipositor enables us very easily, in many cases,
to separate species which are otherwise very nearly
related. Through adaptation to different circumstances,
the ovipositor has assumed many modifications of form,
while the rest of the fly's organization has remained
essentially the same, at least no striking outward
deviations are stamped upon it.

It is interesting to compare the two different genera-
tions from the standpoint of their accepted systematic
classification. So long as classification regarded only
outward marks of distinction, heterogeneous species
were constantly being put into the same genus. In
many classes of insects outward characters alone
might amply suffice to separate the species, because
their various habits of life, and their different adapta-
tions to them, have served to stamp distinguishing
marks upon them ; but in those whose habits of life
differ less, we cannot expect to find aids to classifica-

336 Comparative Classification of Cynipidae.

tion. Therefore by attending only to outward differences,
we may seek out the subtlest distinctions, and yet
obtain no certain basis for a true classification.
Hitherto, for example, the sexual generations belonging
to Ncuroterns and Dryophanta have been united in
the genus Spathegaster ; but one could no more unite
two agamous genera, Neuroterus and Dryophanta, into
one genus, than they could the two forms of Spathe-
gaster. It certainly cannot be denied that the two
Spathegaster forms are alike in outward appearance,
but the two ovipositors show an important difference :
and it is on this character that their separation must
be based. It may be objected that a distinction based
on the form and structure of the ovipositor is too
subtle, but there is no other constant distinguishing
mark. The genus Biorhiza also contains heterogeneous
species. Biorhiza aptera and Biorhiza renum resemble
each other only in outward appearance ; their ovi-
positors are very unlike : and the two sexual genera-
tions belonging to them are so different that they
could not possibly be united in one genus.

Besides the assistance in differentiation which the
ovipositor affords, the manner of gall formation offers
an excellent criterion for determining associated species ;
and with a proper regard to these two features, the
classification of the Cynipidae may be successfully
accomplished. It must be hailed as a step in advance
that analytical tables have been constructed on this
basis; Schlechtendal \ for example, has sketched out
a key to the Cynipidae based on their galls.

^ R. V. Schlechtendal und O. Wunsche, Die Insekten, 1879,

Biorhiza Group. 137

One great difficulty in carrying this out is the fact that
neither the alternate generations nor the gall formations
of all our Cynipidae have yet been discovered. This is
especially the case vi^ith those species living on Quercus
cerris. Here therefore there is still open a wide but
fruitful field of observation.

The food and manner of living among the Cynipidae
present the greatest uniformity, for in all that belongs
to the organs of nutrition, only those modifications
occur which the actual circumstances of life demand,
and hence these organs undergo little variation.

This is especially true of the digestive tract : the
parts composing the mouth are all conformable ; all the
Cynipidae are provided with solid mandibles, in order
to cut through the envelope of the gall, which is often
very hard. The maxillary and labial palpi alone
offer any differences. At first Hartig assigned great
importance to the number of joints in the palpi, and
employed the variation in the number of these joints
as characters. Those given by Hartig have been
adopted in the descriptions of later writers, but there is
great need for their careful revision. Microscopic pre-
parations of these minute organs are rather difficult to
make and have been much neglected. As a rule the
two alternate generations have the same number of
joints in the palpi. Ncurotcrus and the corresponding
Spathegaster have each four joints to the maxillary palpi,
and two joints to the labial palpi ; but the Spathegaster
corresponding to a Dryophanta has, like it, five joints to
the maxillary, and three to the labial palpi. There is
one exception to this rule, in the generation-cycle formed

138 Comparative Classification of Cynipidae.

by Biorhiza renum and Trigonaspis crustalis : here the
number of joints in the palpi varies ; Biorhiza re^mmhsLS
four maxillary and two labial joints, while Trigonaspis
crustalis has five maxillary and three labial.

As regards the joints of the antennae their number
is usually the same in the two generations, except again
in the case of Biorhiza renum and Trigonaspis crustalis,
when the first has thirteen, and the second fourteen
joints in the antennae. There is, moreover, always this
difference in the sexual generations, that the male has
one joint more in the antennae than the female. From
this it will be seen pretty clearly that any characters
based on the number of joints, either in the antennae or
in the palpi, are not to be relied upon.

The intestinal system of the Cynipidae is simple,
uniform in the various species, and very limited in
its functions. My own observations agree with those
of previous observers, and I can confirm the state-
ment that the Cynipidae, in the perfect state, take
no nourishment of any kind, except a little water. The
winter generations almost all appear at a time when
vegetable life is dormant, and offers no sustenance ; but
even the summer generations take nothing except water.

Observation shows that all the Cynipidae require
water, and imbibe it with pleasure. Unless frequent
opportunities of drinking water are afforded, it is
absolutely impossible to succeed in experimental breed-
ing. As regards the summer generations, I will not
deny that they do occasionally lick the juices which
they find on the leaves, but as a rule water is all they
want. On being opened the stomach and metenteron

Biorhiza Group. 139

are generally found empty, or containing only a little
transparent liquid. By chance there may be found,
mingled with this liquid, a little piece of the gall which
has been swallowed in gnawing a way out. The whole
intestinal tract is short and simple, and the Malpighian
vessels are particularly small, few in number, colourless,
and transparent. In gall-flies just emerging, we find in
the last portion of the intestine the excrementitious pro-
ducts accumulated during the larval period, and these
are discharged soon after the flies take wing ; the
quantity is greater in winter generations which pass
through a long larval stage. These excreta are always
liquid and transparent, and it may not be out of place
here to observe, that there is an arrangement by which
regurgitation into the anterior portion of the intestine
and stomach is rendered impossible. In the great
intestine of insects we find certain ridges, the so-called
rectal glands, the use of which, according to Leydig, is
enigmatical.

These longitudinal ridges often differ greatly in form
and number, but are always found in the same situation,
just at the entrance of the great intestine. Leydig
expresses a doubt as to their glandular nature, because
the essential conditions of a gland are wanting, that is
to say, the presence of a secreting epithelium, and the
possession of a duct. He considered them rather as
respiratory organs, since there are, notably in the larva
of the Libellulidae, rectal gills which aid in respiration.
The organs were studied and described afresh by Chun \

^ C. Chun, Rectaldriiscn der Insekten. Verhandlungen d. Sencken-
berg. Gesellsch. vol. x. Frankfurt a. M. 1875.

I40 Comparative Classification of Cynitidae

and he came to the conclusion that they were glands
possessing a specific active secretion ; but it is undeniable
that when the intestine of a gall-fly is exposed, imme-
diately after it emerges from the gall, the function of these
rectal glands appears totally different. Indeed what
we find is, that the termination of the intestine is bulged
into a pouch by the liquid excreta ; and above that, just
where the rectal glands are situated, there is an annular
stricture, and consequently a closure of the intestine.
These glands therefore possess a mechanism analogous
to a sphincter ; now since they project into the intestine,
and are applied one against the other, whenever the
sphincter-like contraction takes place, an obstruction is
produced in the intestine, and the excreta cannot regur-
gitate into the anterior part. Although I have not
pursued narrowly the study of these prominences in
all the other orders of insects, I am able to state, from
the observations I have made, that they are especially
well developed in the case of insects which take liquid
sustenance, such as Hymenoptera, Diptera or Lepido-
ptera, and that they appear to be wholly wanting in the
Coleoptera. Accordingly I assume that these promi-
nences are only intended to aid in the closure of the
intestinal tube ; indeed without them it is difficult to see
how a re-fouling of the anterior part of the intestinal tube
could be avoided, in the case of those insects which ac-
cumulate liquid excreta at the lower end of the intestine.
The small amount of nourishment that the Cynipidae
take, indicates a brief existence as a perfect insect.
Life in both generations is short ; that of the winter
generation is a little longer than the other, some species

Biorhiza Group. 141

living from two to four weeks. Several of the summer
flies are very fragile and do not live many days.

The whole energies of the Cynipidae are devoted to
the proper deposition of their eggs. The more easily
and quickly the eggs can be laid, the shorter is the life of
the individual ; this we see exemplified in Spathegaster.
If on the contrarj' the act of egg-laying is difficult, and
demands much physical exertion, the gall-flies are
stronger and live longer ; the winter generations, which
always have the troublesome task of laying their eggs
in buds, have consequently a much more vigorous
organization than the correspondingsummer generations,
and this also enables them to resist the inclemency of
a ruder season. A Biorhiza aptera fly can prick a bud
with the thermometer at freezing point ; its summer
generation, Teras terminalis, would undoubtedly be
frozen by the same degree of cold.

Lastly it is important to compare the reproductive
organs in the two generations. Here a perfect analogy
will be found to exist ; the ovaries have the same
structure, each contains a corresponding series of
ovarian follicles, in which there lie from six to twelve
eggs. In a general way the agamous generations have
a larger number of eggs than the sexual, and as a rule
the number of follicles, as well as the number of the
enclosed eggs, is greater.

The muscular vagina, with its glandular appendages,
is the same in the two generations. On each side, near
the oviduct, a simple glandular tube opens into the vagina.
Its secretion probably only serves to furnish a liquid
suited to receive the spermatozoa as they escape from

143 Comparative Classification of Cynipidae.

the receptaculum seminis, and to help in conveying them
to the eggs, which they are intended to fertiHze on
entering the vagina. Here also it is the rule that these
glands are much more developed in the sexual species
than in the agamous.

The receptaculum seminis is found in both generations.
It is interesting to note that it is not absent even in
those species which only reproduce themselves partheno-
genetically, although in these fertilization never takes
place ; but on comparison with the receptaculum of sexual
species, it exhibits a certain amount of atrophy. In the
agamous species it appears more or less rudimentary ;
the sac is collapsed, atrophied, and without pigment,
while the glandular appendages are very much reduced
in size. But the constant presence of a receptaculum
seminis shows that, at some antecedent period, males
must also have existed.

There are other phenomena still which indicate this.
If we observe a fly of an agamous generation, as for
example Aphilotrix radicis, just as it has emerged from
the gall, we see that after a few moments, it extrudes the
ovipositor, and remains some time in this position.
Why does it do this? The sexual species does pre-
cisely the same, and the object of this position is clear;
we recognize in it the attitude preparatory to coitus,
which is only, indeed, possible in this way.

Gall-flies with long ovipositors withdraw the whole
of the piercing apparatus into the abdomen in a state of
repose ; if it were possible for fecundation to take place
thus, the penis of the male must necessarily be equal in
length to the coiled ovipositor. But it is infinitely

Biorhiza Group. 143

shorter, so that it is only by extruding the ovipositor
that the vagina of the female can become accessible to the
male. Now, seeing that the agamous generations have
retained the habit of extruding the terebra, as an invita-
tion to fecundation, does this not seem to indicate that,
at some antecedent period, males must have existed ^ ?

We know, besides, that among other Cynipidae, not
living on the oak, a solitary male is occasionally found,
although reproduction is carried on purely partheno-
genetically. I refer to the Cynipidae of the rose, Rhodites
rosae and Rhodites eglanteriae. In both of these there are
found solitary males, although it is probable that for
a long time coitus has ceased to take place.

Lastly, besides those already mentioned there are still
two other accessory glands situated in the vagina, a little
nearer the origin of the ovipositor, which are easily
recognized by their round form and milk-white colour.
They contain an abundant secretion closely resembling
a fatty emulsion, and this secretion, I am inclined to
believe, has the purely mechanical purpose of anointing
the piercing apparatus. In the case of certain other
Hymenoptera (aculeata), we find, at the root of the sting,
an oil-gland which lubricates, with its fatty secretion, the
spot where the two spiculae are jointed into the grooved
seta, and facilitates their to and fro movement. This
oil-gland is wanting in the Cynipidae ; but it is replaced
in them by the pair of glands just mentioned, which are

[* According to Lichtenstein this position so modifies the appearance
of the insect that Radosskoiosky, a Russian naturaHst, has made a
ne%v genus ' Manderstjernia' of acynips having the ovipositor extruded
in this way. Bulletin Soc. Imp. des natural, de Moscow, 1866.]

144 Comparative Classification of Cynipidae.

much more developed. For the long and arduous work
which they have to accomplish, it is indispensable that
the terebra should be well lubricated, so that its functions
may be performed with ease and certainty.

The larval state in the two generations presents also
some variations ; my researches in regard to these are
still fragmentary, and I can only note certain isolated
points. I will begin with the egg and its evolution.

However variable the duration of development
may be after the eggs are laid, as a rule embryonic
evolution begins at once, and it has no prolonged period
of egg-rest. Even in the case of eggs deposited in the
depth of winter, between November and February,
embryonic activity goes on from the first. This evolution
is naturally slower during the cold season, and con-
versely in the summer generations it requires much less
time, but even among these we have examples of an
embryo remaining a very long time in the egg. When
we find that an egg laid in December or January re-
quires some months for its embryonic stage, we can
understand it, because it is only when plant growth
commences, in April or May, that nourishment reaches
the embryo. But why should the same thing occur with,
for example, the eggs of Trigonaspis crustalis laid in the
end of May or beginning of June ? It seems difficult to
explain this long embryonic rest. Three whole months
of this latent existence pass away, and it is not until
September that the embryo bursts the shell of the egg,
and gall formation begins. It is impossible to suppose
that the conditions necessary for gall formation are more
favourable then than they were some weeks or months

Biorhiza Group. 145

sooner ; nay, on the contrary, in September the period
of vegetation is on the wane. The most probable
explanation seems to be that this peculiarity of embry-
onic evolution has been inherited from the generation
Biorhiza aptera, in which the embryonic stage lasts fully
four months.

Yet it is necessary to add that this explanation does
not hold good for all species ; thus, for example, Dryo-
phanta divisa has an embryonic stage even more ex-
tended, for the eggs are laid in October, and the gall
does not develop until May. In the corresponding
summer generation {Spathegaster verrucosus) the galls
are formed at once, and appear four weeks after the eggs
are laid.

The eggs of the two generations, which are necessarily
always unfertilized in the one, and fertilized in the other,
do not present any longer period of rest in the one case
than in the other, but on the contrary all show signs of
commencing embryonic development immediately after
they have been laid. Parthenogenetic eggs, which are
almost always laid in the winter, simply exhibit a much
slower evolution than fertilized eggs, which are always
laid in the summer. Winter eggs thus offer very good
subjects for observation, on account of the slow progress
of the various steps of development ; it is however
a tedious and difficult process to extract them from the
buds uninjured, and to make good preparations of them.
As I have already said, all my attempts to overcome this
difficulty, by endeavouring to secure the evolution of
eggs taken from the ovary direct, have been fruitless.
However simple may appear the circumstances of the

L

146 Comparative Classification of Cynipidae.

deposition in the bud, I have never yet been able to
imitate them artificially. In spite of all the methods
employed I have never succeeded, after many days of
observation, in seeing even the commencement of yolk
segmentation, although in eggs taken from buds I could
always reckon with certainty on seeing this take place
after twenty hours. I have already explained the
important part which the egg-stalk plays at the outset
of embryonic evolution.

The larval stage presents differences in the two genera-
tions, but they only concern the duration of development,
which is very variable. The larvae agree perfectly in
their structure and organization ; as they all live under
similar conditions, no opportunity is offered for any
special or varied adaptation to environment. The
structure of the mandibles alone differs in some species ;
thus the larva of Neurotcrus has strongly toothed man-
dibles, while that of Spathegaster has them simple and
unindented. It is the character of the galls that regulates
these modifications. When the gall substance is hard,
as in the Neurotcrus galls, the larva is found provided
with strong mandibles ; if on the contrary the galls are
succulent and their walls soft, as in the Spathegaster
galls, the mandibles of the larva will be found to be
simple and less powerful.

The duration of larval evolution varies much in the
two generations. In the summer species the larva
increases rapidly, and when full grown passes straight
into the pupa state. In the winter species the larval
stage is infinitely longer, and presents the following
varieties : —

Biorhiza Group. 147

(i) The larva developes during the same year and
acquires its full growth ; then it rests a year, or even
more, in the gall (species of genus Aphilotrix).

(2) The larva during the first year undergoes only
partial development, passes the winter, and does not
complete its evolution until the following year.

(3) Larval development undergoes a period of com-
plete suspension after the larva has left the egg and
commenced to form the gall. It remains dormant some
months, and only begins to grow again when the gall
falls to the ground {Neiiroterus).

The prolonged larva rest of certain species is very
curious ; and that which is especially remarkable is, that
we often see them remain unchanged for three years
before they enter the pupa state. Even among species
which have no alternate generation, there are some galls
from which the fly does not emerge until the third year.
From the regularity with which this occurs, it seems to
be perfectly clear that there are individual differences
in the duration of development, consequently we find that
in the same species some individuals will complete their
development in one year, while others will require two.
The prolongation of the larval stage is a remarkable
phenomenon ; one would rather have imagined that
a short stage would have been of greater advantage to
the species, since the gall would have been exposed for
a less time to danger from changes of temperature. It
is possible for the two generations to complete their
evolution in one year, as in the Ncuroterns-Spathegaster
and the Dryophanta-SpatJiegaster groups. It is inter-
esting to find among the genera which have habitually

L 2

148 Comparative Classification of Cynipidae.

a two-year cycle, a species in which the greater part of
the individuals complete their evolution in one year.

It may perhaps be taken as an indication that at some
former time, when conditions of climate were different,
a long larval stage was the rule, but that little by little
it has diminished, in some already to its full extent, in
some only partially, and in others as yet not at all.
We must also admit the same view to hold good with
regard to the species which have no alternate generation ;
with a certain number of individuals the cycle has become
annual, with others it is still biennial.

CHAPTER VI.

Alternating Generations in Oak Gall-Flies. The Relation-
ship OF THE PaRTHENOGENETIC TO THE SeXUAL GENERATION.

How IS THIS Generation-Cycle to be explained ?

It only remains, in conclusion, to review generally the
subject of alternation of generations in oak gall-flies,
but I would premise that I have chosen the term
'alternating generations'^ without intending in any way
to prejudge the question. It only indicates the posses-
sion of cyclical propagation ; while the different terms
used with regard to this form of propagation, such as
alternating generation, heterogenesis, metagenesis, are,
although all closely related, each used in a different
sense. Lubbock requires, as a necessary condition of
alternating generation, that one generation should pro-
pagate itself by budding, like Aphides ; but with gall-flies
propagation by budding does not take place. Although
parthenogenesis and budding may not differ in principle,
yet there is this important distinction between them, that
in the former, embryonic development runs its entire
course outside, and in the latter, inside the ovarium-
Among gall-flies both generations develop in exactly
the same manner. For this reason I cannot agree with
^ Generationswechsel.

150 Alternating Generations in Oak Gall-Flics.

Lichtenstein, who so ably investigated the Phylloxera,
in assuming that the agamous generation of gall-flies
holds a subordinate position to the sexual generation,
in the way that the budding generations of Phylloxera
and Aphides do to their winged and sexual generations.

The question of the mutual relationship of the two
generations to each other, is of fundamental importance
in the inquiry into the origin of alternation of genera-
tions. It is necessary therefore next to consider par-
thenogenesis, in so far as it has a bearing on alternation
of generations.

When I first discovered the alternation of generations
in gall-flies, I believed in the existence of a definite law,
in accordance with which the gall-flies of one generation
invariably propagated themselves parthenogenetically,
and those of the next generation always sexually. But
more extended observation convinced me that there was
no such universal law. I soon found that some species
continue to propagate themselves by an annual parthe-
nogenesis. This new light led me to investigate more
fully parthenogenesis as it exists in other families of
Hymenoptera, and I will state briefly the result in so
far as of interest to the preceding question.

Parthenogenesis has frequently been observed among
saw-flies. Professor v. Siebold showed, by accurate
observations made on Nonatus vaiiricosus, that parthe-
nogenesis very frequently occurs, although an equal
number of males and females exists in this species.
I have myself closely investigated another species,
Nematus Vallisnierii.

In the autumn of 1876, I collected a large quantity of

Alternating Generations in Oak Gall-Flies. 151

the well known bean-shaped galls of this species, which
are often found very plentifully on Salix amygdalina.
In May, 1877, I reared the flies, and was able to convince
myself that they were all of the female sex. I continued
the experiment by putting them on little willow saplings
set in pots, and soon observed the flies begin to saw the
tender leaves at the end of the shoots, and deposit their
eggs in them. At the beginning of July the full-grown
larvae from the galls buried themselves in the earth, to
assume the pupa state. They remained in this condi-
tion for a very short time, and the first flies appeared on
July 27. Again they were all females, and began at once
to deposit their eggs. By the end of August the galls
were fully developed on the leaves which had been
pricked, and the larvae betook themselves to the ground
in October, to assume the pupa state. In this particular
instance, two generations appear yearly, by strictly par"
thenogenetic propagation ; so that while Nematus ventri-
cosits only occasionally reproduces itself by partheno-
genesis, Nematus Vallisnierii habitually does so. At the
same time, the occurrence of parthenogenesis in Nematus
ventricosus shows that it may proceed directly from
a sexual generation. Probably this occurs more readily
amongst Hymenoptera than amongst any other class
of insects, and therefore I should like to add the
following observations on Pteromalus piiparum.

This little parasite lays its eggs in the pupae of
different lepidoptera, such as Vanessa lo, V. poly-
cJiloros, V, tirticae, Pieris rapae, &c. A single pupa
often supplies more than a hundred of these little flies,
so that it is not difficult to collect a sufficiency of them.

152 Relationship of the Parihenogenetic to

As a rule the males of this species appear first and
may be easily distinguished from the females ; it is
therefore easy to separate the sexes, and so prevent
fecundation. If the unfertilized females are put with
the lepidopterous pupae, they usually proceed to pierce
them at once. I have frequently tried this experiment,
usually with the result that the unfertilized females
only produce males. The result of one experiment
was as follows.

In the spring of 1876, I collected a quantity of Pieris
brassicae pupae which had been pierced by Pteromalus
puparum. At the same time I had reared caterpillars
of Vanessa uriicae which pupated in June. These
pupae were pierced by the unfertilized female Pteromali.
To be quite sure, I examined the rcceptaculum seminis
and was perfectly certain that fecundation had not
taken place. These pierced pupae gave the following
results.

ist Pupa=i24c?. 3rd Pupa = 75c?5P.

2nd Pupa = 62 (^. 4th Pupa =45 (;J4 p.

I will add an instance from the rose-gall Cynipidae,
showing that parthenogenesis is developed directly
from the sexual generation. I have experimented with
both Rhodites rosac and Rhodites eglanteriac. I have
reared hundreds of the former species, and have
received the results of other observers, and they all
show that the males occur in a very small proportion,
about 2 7o only. Owing to the rarity of the males, most
of the females are unfertilized, a fact which is confirmed
by experiment, for all the flies soon after leaving the

the Sexual Generation. 153

galls lay their eggs. The few males that are still
produced are thus superfluous, and we can predict
that they will probably become extinct in the course of
time. In the other species, RJwditcs eglanteriae, some
males have been observed, but after repeated experi-
ments, I have only succeeded in obtaining females.

These facts show that parthenogenesis occurs very
frequently among the Hymenoptera, and that it then
springs directly from the sexual generation. The
result as regards the sex of the offspring is varied, and
appears to be subject to no definite law. Among some
Hymenoptera, especially among bees, males preponderate
when the eggs are unfertilized ; among gall-flies females
usually preponderate \ It appears that where partheno-
genesis has been long continued, males ultimately
become extinct : they are unknown in Nematus Vallis-
nierii, and in several species of Aphilotrix, but it is not
utterly impossible that a male might occur. In the
alternating generations of gall-flies the case is somewhat
different ; the agamous generation occurs only in the
female sex, while in the sexual generation males and
females emerge in equal numbers. Since, however, it is
the agamous generation which produces both sexes, we
may assume, a priori, that in the ovary there are plasms

[* Rolph classifies the offspring of parthenogenesis in groups (i) S
only ; p from fertilized ova (Apidae). (2) One mixed brood
(Cynipidae). (3) Mostly (^ , occasional p (Nematus). 14) Mcstp^
periodic or exceptional (J (Apus). (5) p only (Rotifera).

Ova fertilized by the queen-bee yield workers and queens. If the
nuptial flight be prevented, or the queen be old, and her sperm store
exhausted, the ova yield drones only ; but Blochmann says these ova
show two polar bodies. May these be the first polar body divided ?
If not, is the next generation fertile ?]

154 How is this Generation-Cycle to be explained?

differentiated into the two sexes, and that these have
been inherited from the sexual generation. But with
regard to sexual generations which only produce
females, we may assume that every eg^ w^ithout
exception has been fertilized, and that such eggs, as in
the case of bees, invariably produce females.

If we look at these experiments aright, we perceive
that parthenogenesis has been evolved in different ways,
according to the requirements of each individual case.
It is essential therefore to inquire how each species
has developed its own mode of reproduction.

I had started on my inquiry into parthenogenesis
with the theory that it was on exactly the same level as
sexual propagation, and that there could be no criteria
by which one generation could be subordinated to the
other. But another, and a very important fact, shows
that the two generations of gall-flies are co-ordinate the
one with the other.

When we try to explain the occurrence, at the present
time, of two generations so utterly different from each
other as those we find in the oak gall-flies, we are
obliged to admit unconditionall}^, that originally this
difference did not exist, but that both generations were
similar. For it is a definite law that the offspring
inherits, with the greatest constancy, the organization
and physical form of its parents. If differences arise
between two originally identical generations, we must
refer them to an alteration in the external conditions of
life. Of these we place first change of climate, for we
know from Weismann's experiments on the seasonal
dimorphism of certain butterflies, that differences of

How is this Generation-Cycle to be explained? 155

climate can give the first impulse towards a separation
between the two generations. As for the degree of
difference, that is determined by a factor which we
cannot make use of with exactness. It is essentially the
individual organization of each species, which at one time
inclines it to vary, and at another to remain constant.
Thus we find that, in spite of the most opposite outward
circumstances, almost no difference has taken place in
the generation of one species of gall-fly {aptcra —
tcrminalis); while on the contrary we are struck by the
extraordinary differences which have arisen in those
of another {renum — crustalis).

If therefore the two generations resembled each other
to begin with, which I believe cannot be doubted, the
inquiry which of the two generations is the original, or
which to-day most closely resembles it, becomes of the
greatest interest. With regard to this there are two
important points to be considered :—

(i) Some species are only propagated parthenogene-
tically. (In Chapter II four species are described.)

(2) No species of oak gall-fly is known to propagate
itself exclusively in a sexual manner. They are only
known to do so alternately with an agamous generation
in a generation-cycle.

Therefore it seems to me reasonable to infer that the
present agamous form is either itself the original form,
or if not exactly identical with it, it is at least very
nearly related to it.

There are wider questions still which must remain
unanswered. It cannot be doubted after all that has
been put forward in these pages that parthenogenesis

15*^ How is this Generation-Cycle to be explained?

was a habit which was acquired by degrees, but at what
time it became the rule, would be now as difficult to
determine, as whether originally there were one or two
generations produced in the year. It is probable that
at first there was only one generation developed
annually, as is still the case with the purely agamous
species.

In any case, I consider it certain that parthenogenesis
is the primitive mode, and that sexual reproduction is
subordinate to it.

It is of the greatest importance to the proper
comprehension of the whole subject of alternating
generations, to be able definitely to distinguish one
generation as the primaryone. The important differences
existing between the generations of our time un-
doubtedly demand long periods for their development,
while any certain means for estimating such periods are
wanting. If gall-flies were found among fossil insects,
we should have a definite starting-point, but no such
discovery has been made. We only know that in
earlier epochs a totally different climate to the present
existed ; under the powerful influences of a constantly
though gradually changing climate this remarkable
alternation of generations has been developed, while
the adaptation to new conditions of life has left
the general organization of the species more or less
changed.

A glance at these totally different generations as they
now occur shows above all how difficult is the problem
to seek

*in der Erscheinungen Flucht den ruhenden Pol.'

Hoiv is this Generation-Cycle to be explained? 157

By a few traits only, like hieroglyphics sculptured on
the stones of antiquity, does alternation of generations
demonstrate to us how remote is the period over which
the history of its origin extends.

SCHLESWIG,

May, 1880.

POSTSCRIPT.

However interesting may be the facts of alternation of
generations as they occur in the oak gall-flies, I have no
desire to ignore those species which live on other plants, or
to omit the study of their evolution.

The rose Cynipidae, of which I have observed three
species, Rhodites rosae, eglanteriae, and spinosisshnae, are
always propagated by one annual generation. It is the
same with the species of the genus Aidax, A. rhaeadis and
A. hieracii ; and with those of the genus Diastrophus, D. rubi
and D. glechomae.

On the other hand there is a Cynips.on the maple which
shows absolutely the same biological cycle as the Cynipidae
of the oak. In this species, as in those, one agamous
alternates with one sexual generation.

The following is a description of this insect and the history
of its development,

1, Pediaspis aceris, F6rster= 50;-^/, Tischbein^.

Gall. The gall is found on the roots of the sycamore
{Acer pseudo-platanus), but it is also met with on the Norway
maple (Acer plafanoides). When solitary, the gall is round,
like a pea, and about 5 mm. in diameter. When in clusters,
these are found embracing rootlets, even those of i cm. in

' Dr. Mayr of Vienna, whose works have been of immense service
to the study of the Cynipidae, had previously suggested that the two
species Pediaspis and Bathyaspis aceris were two forms of the same
insect. His breeding experiments, hice my own, have confirmed this
hypothesis.

] 6o Maple gall.

diameter. But they are also found above ground where the
root leaves the tree. When they form a cluster around a
root, they give rise to a regular cylindrical swelling, which
may measure 5 cm. or more in diameter. This gall consists
at first of a firm somewhat fleshy tissue, with a small larva
chamber, like that of Biorhiza aptera. When mature, it
exhibits a wrinkled, woody, brown shell, of no great thick-
ness, enclosing a large cavity.

Experim.ental breeding. The galls mature in Spring,
and are best collected in the month of March. They then
contain the perfect flies, which have wintered in them. In
the month of April they gnaw their way out and quit the gall.

Fly. Length 5 mm. ; colour, ferruginous ; the face, the
parapsidal furrows, a line at the base of the wings, the
middle of the sternum, and the metathorax, blackish ; the
thorax slightly haired above, more strongly so at the sides ;
scutellum depressed, surface rugose, with a narrow smooth
margin ; abdomen smooth, slightly shining, the last seg-
ments darker above ; legs reddish brown, strongly haired ;
antennae with fifteen joints.

Experimental breeding. It is comparatively easy to
rear this fly successfully. My own experiments were made
last April. I began on April 12, having prepared for the
purpose six small trees of Acer pseitdo-platanus in pots.
The flies placed on the trees began at once busily to
examine the buds with their antennae, and prepared to
prick them. Their method of setting to work was rather
remarkable. When a fly had found a bud that suited her,
she placed herself in such a position, head downwards, that
she could drive her terebra diagonally from above towards
the centre of the bud-axis. She pricked the bud several
times, so that a number of eggs were deposited in the
same bud.

I could see with the aid of a lens the openings of the
little canals pierced by the terebra on the covering of the
bud ; and an examination of the buds which had been
pricked, showed that the eggs had been deposited on the
rudimentary leaves. According to this, the galls ought

Sycamore gall. 1 6 1

to develop on the leaf. The first leaves of the pricked
trees, which had been kept indoors, unfolded themselves
on May 15. I was able to ascertain at once the presence
of an abundant formation of galls. One bud alone developed
five leaves on which I counted 14, 9, 6, 4, and 2 galls
respectively.

On four of the trees there were galls, and on two none.
They had however all been pricked alike, but those without
galls were almost a month behind the others in growth;
I therefore inferred that the larvae, when they escaped
from the egg, were unable to find the tissues of the plant
in a condition suitable for their development, and con-
sequently perished. The galls thus obtained were those of
Bathyaspis aceris.

2. Bathyaspis aceris, Forster.

Gall. The gall is formed on the leaves of the sycamore,
exactly as the galls of Spathegaster baccarmn on the leaves
of the oak. As the egg is deposited in the centre of the
bud, on a leaf as yet undeveloped, the structure of the leaf
is always more or less altered by it. As a rule, this
alteration is limited, as far as can be seen, to the galls
growing through and through the leaf, but sometimes when
several galls are situated side by side the leaf is completely
crumpled up. It also occasionally happens that the gall
is developed on the petiole, which then undergoes an
irregular enlargement. The galls which are situated on
the leaves are regularly rounded ; 5 mm. in diameter ;
green or greenish yellow, tinted with red on the side
exposed to the sun ; the surface is very slightly hairy
or quite smooth ; the walls of the gall when mature are
thin, somewhat solid, and enclose the large larva. The fly
emerges at the beginning of July.

Fly. Size 2-2-5 nim. ; brownish yellow, lighter than the
agamous generation. All the body is of the same colour,
except the apex of the abdomen, which is a little darker
above. Villosity apparent on the face and the sides of the
thorax; very feeble or entirely wanting elsewhere. The

M

1 6 2 Sycamore gall.

scutellum depressed, rugose in the centre, surrounded by
a well-marked smooth border. Abdomen shining, legs
yellow. Antennae with fourteen joints in the female, and
fifteen in the male. Colour similar in both sexes.

In this generation the males and females are equal in
number, so that fecundation is secured before oviposition.

I have not hitherto been successful in rearing this
generation ; the fecundated females descend the tree and
set about pricking not only the superficial roots but also
the base of the tree. I have no doubt that these galls
require two years for their development, in the same way as
Biorhiza apfera.

As Pediaspis sorbi, Tischbein, and Bathyaspis aceris both
belong to the same generation-cycle, there is good reason
for abandoning Tischbein's name sorbi. There must have been
some confusion in the first discovery of this gall, for there is
no doubt that it is found only on the sycamore, and not on
the mountain ash as was then stated.

A comparison of the two generations shows a sensible
divergence in size, in spite of natural characters otherwise
sufficiently similar. In the terebrae there is an essential
difference, rendered necessary by the nature of the work to
be done by each. The organization of the two generations
is also quite dissimilar ; the agamous lives three or four
weeks, while the sexual survives but a few days.

Now if we unite the two generations in the same species,
as Dr. Mayr has just done, and with good reason, we ought
to remember that we are uniting two forms which are very
different. According to the ordinary tests of classification
we ought here to make of these two generations what
would be considered two 'good species.' And yet this
would be a wrong interpretation of facts which at present
we must be satisfied to observe. We are still in the stage
of observation ; and it must be left to some future generation
to undertake the explanation of the facts.

SCHLESWIG,

August I, 1 88 1.

APPENDIX I.

Cynips Kollari\ Hartig.

Gall. Size 1-5-3 cm. in diameter, spherical, with a well-
marked base of attachment at one pole, and a small bifid
apex at the other ; beneath this is a linear scar, and around
it a circle of warty elevations.

The galls may be solitary, or two or more together on the
same bud ; and each is situated in the axil of a leaf, or several
may be found crowded together on a terminal bud, in which
case the internodes have been suppressed. The gall contains
a central elipsoidal larva chamber, which retains its shape
even when the gall itself is compressed and flattened by the
growing shoot. The gall appears in June, is golden yellow
if grown in the shade, and green if exposed ; it matures in
September, and becomes brown as the outer layers dry. In
this state it may hang on dead branches for three or four
years, but the growth of living wood detaches it sooner.
If a transverse section of a young gall, 3 mm. in thickness,
be made at the end of June, it will be found, according to
Beyerinck, to exhibit the following structure : a larva chamber
surrounded by (i) a thin layer of primary nutritive tissue,
(2) a thin layer of cells containing crystals, (3) a thin layer
of primary starch cells, (4) the layers of the cambium ring,
(5) a thick layer of large cells rich in tannin and traversed
by vascular bundles, (6) a layer of small meristematic cells,
(7) colourless hypodermal cells, (8) epidermis with uni-
cellular hairs containing red pigment in their cell contents.
In the middle of July the epidermis is thrown off, leaving

^ Mistaken by Marshall and others for Cynips Ugnicola, Htg., which
is not a British species.

M 3

164 Appendix /.

the gall of a grass green colour. By August the primary
nutritive tissue has disappeared, and secondary nutritive
tissue, containing proteids, oil globules, and the so-called
brown-bodies, is formed at the expense of the starch. The
gall remains soft until almost mature, but at this time, if it be
.pierced by a needle, a sclerenchymatous layer can be detected
covering the nutritive tissue, giving a certain hardness to the
larva chamber, and affording a protection against parasites.

The larva chamber is normally single, but occasionally,
where the gall-maker has been destroyed, it is found divided
radially into several cells inhabited by parasites. The
inquilines are usually found in larva chambers arranged
around the central chamber, between.it and the surface.
When twin galls are formed closely together, they occa-
sionally unite and have one larva chamber \

Fly. Length 48-6 mm. Whole body reddish yellow.
Looked at from above, the head appears widened behind the
eyes ; cheeks half as long as the eyes, without wrinkles ;
antennae filiform, thirteen-jointed, second joint longer than
thick, third joint the longest, twelfth and thirteenth joints
partially united. Thorax brown, covered with short hairs,
parapsidal furrows complete ; scutellum with two thickly
haired foveae at its base, metanotum black, vertical, over-
hung by the scutellum. Abdomen smooth and shining ;
second segment covering half the dorsum, very dark above,
with two large hairy spots ; the other segments fringed with
silky hairs. Ovipositor long and spiral. Venter exposed.
Wings as long as the fly, hyaline, finely haired ; radial
cellule open at the margin, elongate, with the areolet opposite
its base; basal abscissa of the radius angled ; cubitus opposite
to, but not reaching, the middle of the transverse basal nervure ;
legs yellow, margin of the fore tibiae fringed with short
depressed hairs ; hind coxae broad ; claws bifid. According
to Mayr the fly closely resembles Cynips corruptrix Schl. ;

^ Lacaze-Duthers, ' Recherches pour servir a I'histoire des galles,'
Ann. Sc. Nat. Bot. 1853, P- 291. Beyeriiick, M. W., Beobachtungen
tiber die ersten Entwicklungsphasen einiger Cynipidengallen,
Natuurk. Verh. der Koninkl. Akadentie, Deel xxii.

Cynips Kollari. 165

C aries Gir. ; C. lignicola Htg. ; C. tindoria ; C. caliciformis
and C. galeata, Gir. : species only to be distinguished from
each other by their galls.

Rearing the fly. The mature galls are collected in
September or October, about which time the fly will be
found lying with its head towards the equator of the gall in
the direction of most easy exit. Where the gall is double, it
occasionally happens that a fly gnaws its way into the twin
gall. The flies emerge during September and October, live
about a month, and prick the buds, laying about 800 eggs.
Some flies winter in the galls, and emerge from the end
of April to the beginning of June. The large double galls
with one larva chamber usually afford only one small gall-
maker. If the larvae be removed from the galls in August,
after the nutritive tissue of the gall has been consumed, they
will be found to complete their development in small pill-
boxes, as perfectly as if they had been left in the galls. The
parasites and inquilines as a rule emerge in the spring.

Experimental breeding. In 1857 Mr. F. Smith of the
British Museum had a bushel and a half of the galls from
Devonshire ; the flies from these began to emerge in April,
and continued to do so till the end of May. He obtained
12,000 examples, all of which were female. He placed
sixty galls in separate boxes, and, as soon as the flies came
out, he carried the boxes to different localities in the vicinity
of London, and placed them on low oak scrub. He revisited
the localities in August, and found galls on the same trees in
eight cases out of twelve, but no galls on any other trees in
their neighbourhood. From these galls he again obtained
the same Cynips and once more placed it in isolated situations,
with the result that gaUs were again obtained in the same
proportion as before. In no case could there have been, he
says, 'any connexion with the male sex, unless that sex be
of microscopic dimensions \'

In the autumn of 1881, Beyerinck enclosed a number of
flies in nets of muslin, strained on wire frames, and these

^ Zoologist 7332, quoted also in The Entotnologist, vol. vii. p. 251 ;
1874.

1 66 Appendix I.

he secured around suitable oak twigs. He never actually
succeeded in seeing the egg laid, as the flies are shy in
confinement ; and in hundreds of buds which he examined
he cnly found the tgg in four, and some of these were found
the first day the flies were in the nets. The egg is 2-5 mm.
long, and can therefore be easily recognized.

On May 28, 1882, the first sign of gall formation was visible.
On June 9, the larva was completely walled in, and the larva
chamber closed on all sides. In July the tissues above the
scar died and dropped off, leaving the bifid apex uncovered,
and disclosing a gall 10 mm. in diameter of a grass green
colour. In September growth was complete, and in October
the gall-fly emerged.

C Kollari as a rule seeks out a weakly shoot in October,
and pierces the petiole of the lowest rudimentary leaflet
of a bud, depositing its egg laterally, on the front of the
petiole, and between it and the little secondary bud about
to form in the axil of this leaflet. A blastem grows up
around the egg-body, gradually closing over it, and pressing
the larva out of the egg-shell, which is held back by the stalk.
As the petiole of the leaf grows, the canal, with the egg-stalk
in it, is carried upwards, and the egg-shell is thus torn out
of the blastem.

The gall of C. Kollari is widely distributed in Italy, France,
Austria, Holland, and in Germany as far north as the Elbe.
In England it appears to have been introduced at Exmouth
about fifty years ago at a time when cloth manufacture was
extensively carried on in Exeter, Tiverton, and other towns
in the west of England ; but whether the gall was first
imported for dyeing purposes is not known. Canon Derham
does not mention having found it, although he was well
acquainted with the Aleppo gall. It spread slowly over the
county, and from this circumstance it came to be called the
Devonshire gall.

Cynips Kollari created quite as much sensation in its time
as the Colorado beetle or the Hessian fly. As late as 1852
it was averred that the gall was utterly destroying the crop
of acorns, used for feeding pigs, and that the loss to farmers

Cynips Kollari. 167

would be enormous. Labourers were exhorted to ' rally
round the pig.' The destruction of the oak and the ruin
of the wooden walls of England were predicted, and it
was stated that 'the mischief has increased so alarmingly
that unless some effectual stop can be put to the evil, the
landowners of Devon, Cornwall, Dorset, Somerset and even
Gloucester will have to abandon all hope of raising oak
timber \' Those who were less easily alarmed pointed out
that the galls contained, even when dry, 17 per cent, of
tannin, which was a third of that contained in the best
Aleppo galls, and as they generally grow within ten feet
of the ground, it was only necessary to collect them for
ink-making in order to bring about their speedy disappear-
ance. As to the injury to the acorn crop, it was shown that
the Cynips prefers young trees or scrub, while an oak
seldom produces acorns until it is fifty years old ; so that
although few acorns were found on galled trees, those were
trees on which no acorns were to be expected.

The gall has now spread steadily over the whole of England
and Scotland. In hard winters titmice and squirrels destroy
large numbers of them, cracking them up and picking out
the larvae.

Inquilines. Synergus Reinhardi, S. melanopus in May and
June of second year. S. pallicornis from April to June of
second year. S. facialis and Ceroptres arator.

Parasites. Torymus regitis {Devoniensis), Megastigmus
stigmaticans, Decatotna ?sp., Macrocentrus marginator.

Mr. Fitch ^ gives the following parasites : Ormyrus
punctiger, 18 June — 29 July; Eurytoma ?sp., 18 April;
Pkromalus tibialis, Callimome ?sp., 28 April — 20 June ; Calli-
mome ?sp., 3-17 April ; Entedon ?sp., Eurytoma rosae,
Syntomaspis caiidata, Honialiis aitratits, H. coeruleus, Odynerus
trifascatus and the bee Prosopis rupestris.

Many insects pupate in the empty galls ; these include,
besides hymenoptera, numerous lepidoptera and beetles.

^ Mr. Rich at Entomol. Soc, London, Nov. 6, 1854. Entofnol. vol.
vi, pp. 275-338 ; vii, p. 245 ; Gardeners Chronicle, 1854, p. 742 ;
1855, p. 789 ; i860, p. 72 ; 1862, p. 813.

^ Entomol. 1879, p. 113.

APPENDIX II.

SYNOPTICAL TABLE OF OAK GALLS.

L On the Leaf.

A. On the under surface of the leaf.

(a) Currant-like, green often tinged with crimson, less

than 6 mm. in diameter, in May and June.
Smooth and glabrous, 5-6 mm.

I*. Spathegaster baccamm.

Pale, 4 mm., covered with erect white hairs falling

off at maturity. 4*. Spathegaster tricolor.

(b) Cherry-like, 1-2 cm., July — Oct.

14. Dryophaiita scutellaris.

5-7 mm., red with white stripes, skin rough and

nodular. 15. Dryophanta longiventris.

(c) Like buckshot, broader than high, smooth, shining,

red becoming brown, July — October.

16. Dryophanta divisa,
{d) Ovoid, smooth, greenish, then brown with red

spots, on vein, between two brown scales, Aug.

and Sept., 2-3 mm. 19. Neuroterus ostreus.

[e] Kidney-shaped, 1-2 mm., green, crowded on veins,

in September and October. 18. Biorhisa rectum.
(/) Flat, circular, lenticular, often irregular.

Sunk in the leaf-substance, green, radiate striation,

May and June. 3*. Spathegaster vesicatrix.

Synoptical Table of Oak Galls. 169

Not sunk, attached by a point, covered with
golden silky hair, round, centre depressed, in
Autumn. 3. Neuroterus numismatis.

Not covered with golden silky hair, flat, almost

glabrous, margins turned up, centre bossed.

2. Neuroterus laeviusculus.

Covered with stellate hairs, top convex.

I. Neuroterus lenticularis.

Top concave, bottom pilose, edges curled up.

4. Neurotetus fumipennis.

B. On margin of the leaf.
No inner gall :

ovoid, smooth, 1-2 mm., June and July, N. albipes.
spindle-shaped
shortly - stalked, green with red ribs, apex
pointed, 6-8 mm.. May — June.

20. Aphilotrix seminationis.

not stalked, oval, granular, glossy, green or
reddish, spotted, brown when old, 4 mm.,
May, on half-grown leaves, shoots or buds.

16*. Spathegaster verrucosus.
glabrous, green striped with red, longitudinally
ribbed, 4-5 mm.. May and June, on fully
developed leaves, always sessile.

21. Aphilotrix marginalis.

With an inner gall :

Irregular, round or oval swelling at base of leaf,
green with large cavity containing small brown
inner gall in May. 9*. Andricus curvator.

C. In the midrib or leaf-stalk.

Small elongated tumid thickening of mid-rib or
leaf-stalk. 6*. Andricus testaceipes.

II. On Buds.

Polythalamous : large spongy, apple-like, on terminal
buds in May. i^^. Teras terminalis.

170 Appendix II.

Monothalamous : in May, waxy, not spongy, on twigs
on trunk or near ground, 5-7 mm.

18^. Trigonaspis crustalis.

Pilose and ovate.
Violet with short velvety pubescence in May or
June, 2-3 mm. 14=*. Spathegaster Taschenbergi.

Greenish, 2 mm. May and June.

15*. Spathegaster similis.
Like marbles, on twigs, dark green or brown,
1-5-3 cm., June — September. 24. Cynips Kollari.
Small ovate or elongate, dropping when mature :
Glabrous —

Spindle-shaped, longish peduncle, 7-12 mm.,
green with red ribs, July and August.

11. Aphilotrix callidoma.

Peduncle short, September and October, 6-8 mm.

12. Aphilotrix Malpighii.
Gall not enveloped in leaf-scales :

Small, granular, 1-2 mm., green then brown,
June — August. 7*. Andricus gemmatus.

Obovoid, green with white spots, pointed apex,
5-6 mm.. May and June.

23. Aphilotrix albopunctata.

Gall wholly enveloped in leaf-scales :

Hop-like 20 mm. 10. Aphilotrix fecundatrix.

Gall partially enveloped in leaf-scales :
Gall pea-like, green, thin-walled, April or May.

19*. Spathegaster aprilinus.
Globular, tapering to apex, hard and woody,
September, 3-4 mm., green, smooth when young,
and reticulated when old, apex only appearing
beyond bud, blunt. 8. Aphilotrix globuli.

Ovoid apex pointed and darker than rest of gall,
Sept. 9. Aphilotrix collaris.

Apex not ending in dark point, October.

13. Aphilotrix autumnalis.

Synoptical Table of Oak Galls. 1 7 1

Apex of a terminal twig inflated, longer than broad,
large cavity with loose, small inner gall, June.

8*. Andricus inflator.
Irregular swellings on twig, petiole, or mid-rib, June.

'^. Andricus noditli.

III. On Roots.

Polythalamous, woody when mature, large, brown,
irregular, 1-3 inches, on roots, Oct.

5. Aphilotrix radicis.

Monothalamous : on rootlets, often in clusters, irregular,
Sept. 17. Biorhiza aptera.

IV. On Bark and thick Roots.

Or on scars, egg-shaped, becoming honey-combed
when old. Sept. 7. Aphilotrix corticis.

On young branches, hke barnacles, red when young,
brownish when old, often covered with gummy
secretion, June — Aug. 6. Aphilotrix Sieboldi.

V. On Catkins.

In a mass of woolly hair.
Mass agglomerated, dense, 20 mm., June.

13^. Andricus ramuli.
Hair scanty. May and June.

II*. Andricus cirratus.
Not in a mass of woolly hair.

Pilose, brownish, 2 mm., oval. May and June.

10*. Andricus pilosus.
Glabrous :

Currant-like, May. i*. Spathegaster baccarum.

Spindle-shaped, short peduncle, green with red ribs,
apex pointed, 6-8 mm.. May and June.

20. Aphilotrix seminationis.
Obovoid, ribbed sides, base not contracted, 3 mm.,
May. 22. Aphilotrix quadrilineata.

Sides not ribbed, 1-2 ram., in May.

12^ Andricus nudus.

APPENDIX III.

CLASSIFICATION OF THE CYNIPIDAE\

WITH THEIR FOOD PLANTS'^.

GENUS.

1. EscHATOCERUs, Mayr.

E. acaciae, Mayr (Acacia), South America.

2. Pediaspis, Tischbein=BATHYASPis, Forster.

P. sorbi, Tischb., agamous form of the sexual
B. aceris, Forst. (Acer pseudo-platanus), Europe.

Species with alternate generations.

3. Belenocnema, Mayr.

B. Treatae, Mayr (Quercus virens), N. America.

1 In the case of species with alternate generations the two names
under which they were formerly known are retained. The genera
and species are described in Prof. Mayr's monographs and in
Cameron's Phytophagous H ynienoptera, Ray Society.

^ Where the food plant is Quercus robur, so far as the facts have
been recorded, the particular trees on which the galls grow have been
mentioned in the notes, but it is not to be understood that they are
never found on other varieties. The most common variety in England
is Quercus pedunculata ; it is recognized by the leaves being sessile or
nearly so, their upper surface being slightly polished, and by the
acorns having long peduncles. In Q. sessiliflora the acorns are
sessile ; while the leaves are on long stalks and have their upper
surfaces highly polished. Q. pubescens is like the latter variety, but
has a smaller leaf with a woolly under surface. Oaks usually begin
to flower when about thirty years old, but flowers are occasionally
found in a very dry season on much younger trees.

Classification of the Cynipidae. i j-

GENUS.

4. Rhodites, Hartig.

bicolor, Osten-Sacken (Rosa) N. America.

centijolia, Hartig ( „ ) Europe.

dichloceros, O.-S. ( „ ) N. America.

eglanteriae, Hart. ( >> ) Europe.

Mayri, Schlecht. ( j> ) »

rosae, Lin. ( » ) >>

rosarum, Giraud ( >> ) »

spinosissimae, Giraud ( „ ) „

verna, O.-S. ( ,, ) N. America.

ignota, O.-S. ( jj ) »

TiMASPis, Mayr.

lampsanae, Kursch (Lapsana communis).

Phoenixopodos, Mayr (Phoenixopus vimineus),
France (sea-shore).
Phanacis, Forster.

centaiireae, Forst. (Centaurea scabiosa), Europe.
AuLAx, Hartig.

areolahts, Giraud.

glechomae, Lin., Hart. (Glechoma hederacea).

graminis, Cameron (Triticum repens).

hieracii, Lin., Bouche = SaZ»fl«fl?ie', Hart. (Linaria vulgaris,
Hieracium murorum, H. umbellatum).

hypochoeridis, Kieffer (Hypochoeris radicata).

jaceae, Schenck = «^;»5, Schenck (Centaurea jacea).

Kemeri, Wachtl (Nepeta pannonica).

Lichtensteinii, Mayr (Centaurea salmantica).

minor, Hart. (Papaver rhoeas).

papaveris, Perris (Papaver dubium).

rhoeadis, Hart. (Papaver rhoeas).

Rogenhoferi, Wachtl (Centaurea scabiosa).

salviae, Gir. (Salvia officinalis).

scabiosae, Gir. (Centaurea scabiosa).

scorzonerae, Gir. (Scorzonera humilis).

serratidae, Mayr (Serratula heterophylla).

tragopoginis, Thorns. (Tragopogon major).

valerianellae, Thorns. (Valerianella olitoria).

174 Appendix III.

GENUS.

8. Xestophanes, FoRSt.

potentillae, Vill. = abbreviatus, Thorns. ? (Potentilla

reptans).
brevitarsis, Thorns. = Tonnentillae, Schlecht.
foveicollis, Thorns. (Potentilla reptans).

9. Periclistus, Forst. Inquilines of Rhodites galls.

Brandtii, Ratz.

caninae, Hart.

sylvestris, O.-S. N. America.

pirata, O.-S.

10. Rhoophilus, Mayr.

Loewi, Mayr (Rhus lucidum), Africa.

11. Ceroptres, Hartig (Inquilines, lodger parasites).

arator, Hart.
cerri, Mayr.
clavicornis, Hart.
melanocerus, Hart.
socialis, Hart.

12. Synergus, Hartig (Inquilines).

albipes, liart. = eryt/irocerns, Hart.

apicalis, Hart. = immarginatus, Hart. = etythrostomus,

Hart.
evanescens, Mayr.
facialis, Hart = bispinus, Hart.=Diplolepis gallae pomt-

formis, Boyer de Fonscolombe.
yiavipes, Hart.

Hayneanus, Hart. = rugulosus, Hart.
incrassaius, Hart.
lignicola, O.-S. N. America.
melanopMS, Hart = Diplolepis rufipes, Boy er = Sytjetgus

orientalis, Hart.=S. socialis, Hart.
neruosus, Hart. = S. tibialis, Hart. = S. nigricornis,

Hart.
pallicornis, Hart. = S. aiistralis, Hart. = S. nigripes,

Hart.

Classification of the Cynipidae. 175

GENUS.

12. Synergus {continued).

pollidipennis, Mayr.

physoceras, Hart.

radiatits, Mayr.

Reinhardi, Mayr.

rotmidiventris, Mayr.

ruficornis, Hart.

Thaumacera, Dalman = S. Klugi, Hart. = S. luteus

Hart. = S. can'naius, Hart.
iristis, Mayr.
Tscheki, Mayr.

variabilis, M ay r = Diplolepis gallae pom ifonnis, B oy e r .
varius, Hart.
vulgaris, Hart.

13. Sapholytus, Forst. (Inquilines).

connatus, Hart.=S. erythroneurus, Hart.
Haimi, Mayr.
undidatus, Mayr.

14. Synophrus, Hartig.

politus, Hart.

15. DiASTROPHus, Hartig.

cuscutaeformis, O.-S. America.

Mayri, Reinhard (Potentilla argentea), Europe.

nebulosus, O.-S. America.

potentillae, Bassett. America.

radicum, Bassett. America. (Rubus villosus.)

rubi, Hart. (Rubus caesius, fruticosus, and Pteris

aquilina), Europe.
turgidus (Rubus strigosus).

16. Amphibolips, Reinhard.

ilicifolia, Bassett. America. (Quercus ilicifolia.)
inanis, O.-S., Bassett. America.
prunus, Walsh. America.
sculpta, Bassett (Q. rubra et ilicifolia).
spongifica, O.-S., sexual form of C. aciculaia, O.-S.
(Q. tinctoria).

J 76 Appendix III.

GENUS.

17. Andricus, Hart. = Callirhytis, Forst. = Aphilotrix,
Forst.

Species with alternate generations.

AGAMOUS. SEXUAL.

Aphilotrix Andricus

A. atitmnnalis, Lin., alternates with A. ramuli.

A. callidoma, {(^ot^cir.)} " " A. cirratus.

A. collaris, Hart. „ „ A. curvator.

A. corticis, Lin. „ „ A. gemmatus.

A.fecundatrix, Hart. „ „ A.pilosus.

A. globuli, Hart. „ „ A. inflator.

A. Malpighii, Adler „ „ A. midus.

A. radicis, Fal. „ ^^ A. noduli.

A. Sieboldi, Hart. ,, ,i A. testaceipes.

Species of which the alternate generations are yet unknown.
Agamous.
albopunctatus, Schlecht.
callidojna, Giraud (not Adler).
clementinae, Giraud.
glandulae, Hartig.
kirschbergi, Wachtl.
lucidus, Hart.
marginalis, Schlecht.
Mayri, Wachtl.
quadrilineattts, Hartig.
rhisomae, Hart.
Seckendorffii, Wachtl.
seminationis, Adler.
serotinus, Giraud.
solitarins, Fonscol.
urnaeformis, Mayr.

Sexual.
Adleri, Mayr.
aestivalis, Giraud.
amenti, Gir.
burgiindus, Gir.

Classification of tJie Cynipidae. 177

GENUS.

17. Andricus [continued),
circulans, Mayr.
crispator, Tschek.
crypiobius, Wachtl.
cycioniae, Gir.
grossitlariae, Gir.
multiplicatus, Gir,
occiiltiis, Tschek.
Shrockingerii, Wachtl.
singuhis, Mayr = singulans, Mayr.

American Species.

acinosns, Bassett.
calif ornicits, Bassett.
capsula, Bassett.
concinniis, Bassett.
flocci, Walsh.
forticoriiis, Walsh.
ignohis, Bassett.

Osten-Sackenii, Bassett (Q. ilicifolia et coccinea).
petiolicola, Bassett (Q. bicolor).
singidaris, Bassett (Q. rubra).
tubicola, O.-S.

SuB-GENUS CaLLIRHYTIS.

European Species,
glandimn, Gir.
Hartigi, Forst.

American Species,
agrifoliae, Bassett.
clavula, Bassett (Q. alba).
cornigera, O.-S. (Q. palustris).
futilis, O.-S. (Q. alba).

operator, O.-S., sexual of C. operatola, Riley, Q. ilicifolia.
punctata, Bassett.
quercus palustris, O.-S. ?

scitula, Bassett (Q. coccinea, rubra et tinctoria).
N

17^ Appendix III.

CKNL'S.

17. Andricus {continued).

seminator^ Harris (Q. alba).
similis, Bassett (Q. ilicifolia).
spongifica, O.-S. (Q. tinctoria).
Suttoni, Bassett.
titmifica, O.-S.

18. Cynips, Lin., Hartig.

acicitlata,O.S., againous f orm of A. spongi/ica, O.-S.

amblycera, Gir.

argentea, liart. = Hosenkaueri, Hart.

ories, Gir.

calicifort)iis, Gir.

calicis, Burgsd.

caput-tnedttsae, Hart.

conglomerata, Gir.

conifica, Hart.

coriaria, Hart.

corrttptrix, Schlecht.

galeata, Gir.

glutinosa, Gir.

Hartigii, Kollar.

Hungarica, Hart.

inanis, O.-S. (Q. rubra).

Kollari, llart. = Hispanica, Hart.

lignicola, Hart.

operatola, Riley, agamous form o{ A. operator, O.-S

polycera, Gir.

prunus, Walsh.

strobilana, O.-S.

tinctoria, Lin.

19. Aphelonyx, Mayr.

cerricola, Gir.

20. AcRASPis, Mayr.

erinacei, Walsh.
pezomachoides, O.-S.

Classification of the Cynipidae. 179

GENUS.

21. Trigonaspis, Hartig=BioRHizA, Westw. partim.

Species with alternate generations.

crustalis, Hart., alternates with the agamous B.

renum,
synaspis, Hart.

22. BiORHizA, Westw. = Apophyllus et Teras, Hart.

= Dryoteras, Forster.

Species with alternate generations.

aptera, F., alternates with sexual Teras terminalis

(Quercus, Fagus, Pinus, and Vitis),
forticornis, Walsh, American.

23. Chilaspis, Mayr.

nitida, Giraud.

24. Plagiotrochus, Mayr.

cocciferae, Licht.
ilicis, Licht.

25. LoxAULUs, Mayr.

mammula, Bassett. N. America.

26. Dryocosmus, Giraud = Entropha, Fdrster.

cerriphilus, Gir.
nervosus, Gir.

27. HoLCASPis, Mayr.

duricoria, Bassett. N. America. Q. bicolor.
globulus, Fitch.
rugosa, Bassett.

28. Dryophanta, Forster =Liodor A, Forst.

Species with alternate generations.
Agamous. Sexual.

D. divisa, Hart, alternates with the sexual Sp. verrucosa,
scutellaris, Hart. „ „ Sp. Taschenbergi.

longiventris, Hart. „ „ Sp. similis.

N 2

i8o Appendix III.

GENUS.

28. Dryophanta [continued).

Species ofivhich the corresponding generations are yet unknown.

European.
D. agama Hart.
cornifex, Hart.

cylindrica, Licht. on Q. coccifera.
dysticha, Hart.
Jlosculi, Gir.
pubescentis, Mayr.

American.
D. bella, Bassett.
gemmula, Bassett.
nubila, Bassett.

29. Neuroterus, Hart. = Spathegaster, Hart. = AMERisTUS,

Forst. = Manderstjernia, Radoszkowsky.

Species with alternate generations.

Agamous. Sexual.

N.fumipennis, Hart, corresponding to 5/. tricolor, Hart.
N. laeviusculus, Schenck „ „ Sp. albipes, Schenck.

N. lenticularis, Oliv. „ „ Sp. baccarmn, Lin.

N. numismatis, 0\W. „ „ Sp. ves!catrix,Sch\echt.

N. ostreus, Htg. „ „ Sp. apriUniis, Gir.

Species of which the corresponding generations are not yetknoivn.
European.

Agamous.
lanuginosus, Gir.
macropterus. Hart.
saltans, Gir.

Sexual.
aggregatus, Wachtl.
glandiformis, Gir.
obtectus, Wachtl.
Schlechtendali, Mayr.

Classification of the Cynipidae. i8i

JENUS.

29. Neuroterus {continued).

American.

batata, Fitch (Q. alba).
Jtoccosus, Bassett.
ntajalis, Bassett (Q. alba).
minutus, Bassett (Q. alba).
noxiosus, Bassett.
Riteyi, Bassett,
vesicuta, Bassett.

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INDEX

Abdomen, configuration of, 26.
Acari, 77, 78.

Agamous, primitive form, 155.
Agathyllus, 77.
Aleochara, 77.

Alternating generations, table
of, 95.

advantages of, xxxii.

distinction in form, 26.

heredity in, 154.

mutual relations, 150.
Ameristus, 9.
Amphimixis, xix.
Andricus albopunctatus, 93.

ambiguus, 91.

callidoma, 52.

cirratus, 52, 53, 54, 95, 133.

coUaris, 44.

corticis, 37, 39.

curvator, xxxiii, xxxvii, xl,
II, 45, 47, 95, 105.

fecundatrix, 47, 50.

flavicornis, 91.

gemnaatus, 39, 95.

glabriusculus, 91.

globuli, 40, 43, 44, 58.

inflator, xl, 42, 43, 44, 95.

marginalis, 90.

noduli, 30, 31, 33, 35, 36, 95,
126, 132, 133.

nudus, 56, 57, 95.

ostreus, 84.

pedunculi, 91.

perfoliatus, 46.

pilosus, 50, 95, 105.

quadrilineatus, 91.

radicis, 28, 31.

Andricus ramuli, xxxvi, 57, 59,
60, 95.

seminationis, 87, 91, 96.

Sieboldi, 36.

testaceipes, 35, 36, 95.

trilineatus, 31.

verrucosus, 91.
Angiostomum nigrovenosnm,

xvi.
Angular plate, 11 1 .
Antennae, 138.
Anthocoris nemorum, 77.
Anthomyia canicularis, 60.

gallarum, 81.
Ants, xxxvi, 37, 104.
Aphidius, 77.
Aphilotrix, 8, 28, 153.

albopunctata, 93, 94, 96.

andricus group, 132.

autumnalis, xxxiii, xl, 57-60,

95-
callidoma, 52, 54, 55, 56, 87,

95-
coUaris, xl, 44, 47, 48, 95,

104.
corticis, 37, 38, 40, 95.
fecundatrix, xxxvii, xl, 47,

49' 50, 52. 95> 104. 121.
gemmae, 47.
globuli, xxxiii, xl, 40, 4?,

57. 95-
Malpighi, 55. 57, 95.
marginalis, 90, 91, 92, 96.
quadrilineata, 54, 87, 90, 91,

93, 96-
radicis, xxxiii, xxxvii, xl, 28,

30-32, 35.95, 132.

193

Index.

Aphilotrix, seminationis, 87, 89,
91,96.

Sieboldi, xxxiii, xxxvi, xl, 34,
38, 95, 104.

solitaria, 85.
Apanteles breviventris, 79.
Apophyllus, 71.
Arachnidae, 77, 78.
Artichoke gall, 50.
Ascaris megalocephala, xxviii.
Atropos, 77.
Aulax fecmidatrix, 50.

hieracii, 159.

rhoeadis, 159.

syncrepidus, 86.
Autumn gall, The, 59.

Balaninus villosus, 74.

glandium, 77.
Bald seed gall, The, 57.
Balfour, F. M., xxvi.
Bark gall, The, 39.
Barley-corn gall, The, 89.
Bassett, H. F., xiii, xiv, 3, 4, 5.
Bathyaspis aceris, 161.
Bees, parthenogenesis in, 153.
Benecke, xxx.
Beyerinck, M. W.,xiv, xxxiii, 73,

85.
Biennial galls, 109.
Biophors, xxiii.
Biorhiza, 8, 71, 134.

aptera, xxxiii, xl, 71, 73, 76,
95, loi, 124, 127, 134,

145-

renum, xxiv, xxxiii, xxxvii,
xl, 79, 80, 83, 95, 134,
138.
terminalis, 71.
Blastem, xxxvi.
Blastoderm, 4.
Blister gall, The, 22.
Boveri, on male parthenogenesis,
xxii.
on polar cells, xxvii.
Bracon aterrimus, 63.

caudatus, 79.
Bud gall. The, 40.
Buds, adventitious, 62.

selection of, 121.
Butschli, on polar cells, xxvii.

Callimome antennatus, 63.

autumnalis, 77, 78.

chlorinus, 77.

cingulatus, 77, 78.

confinis, 77, 78.

exilis, 77.

fuscicrus, 81.

inconstans, 50, 77.

latus, 77.

leptocerus, 77, 78.

leucopterus, 77, 78.

longiventris, 66.

minutus, 77, 78.

mutabilis, 77, 78.

nigricomis, 78.

parallinus, 77.

rubriceps, 84.

viridissimus, 77, 78.
Cambium ring, 98.
Cameron, P., xiv, 54.
Carpallnus fuliginosus, 77.
Carpocapsa Juliana, 50.
Catkin galls, 49.
Cecidomyia, xvi, 77, 99.
Ceraphron, 77-
Ceroptres arator, 34, 37, 60, 86,

167.
Cetonia, 77.

Chaetochilus sylvellus, 77.
Chamisso, xv.
Cherry gall. The, 63.
Chromosomes, xxiii, xxxix.
Coitus, preparation for, 142.
Collared gall. The, 46.
Commensals, xii.
Corticaria transversalis, 77.
Cotton gall. The, 60.
Cryptidae, 122.
Cryptophagus collaris, 77.
Cryptus hortulanus, 79.
Cuckoo- flies, xii.
Curculionidae, 74-
Currant gall. The, x, 17.
Curved leaf gall, The, 47.
Cynipidae, xiv, 172.
Cynips aciculata, 2.

albopunclata, 93.

aries, 165.

autumnalis, 57.

callidoma, 52.

calyciformis, 165.

Index.

193

Cynips, calycis, xxxvi.
collaris, 44.
corruptrix, 164.
corticalis, 34.
corticis, 37.
ciustalis, 81.
curvator, 46.
divisa, 67.
fecundatrix, 47.
folii, 60.
galeata, 165.
gemmae, 47.
globuli, 40.
glutinosa, xxxvi.
inflator, 43.
inflorescentiae, 87.
Kollari, xvii, xxvi, xxxiii,

xxxvii, xl, 96, 163.
lenticularis, 9.
lignicola, 165.
longiventris, 64.
majalis, 93.
marginalia, 90.
megaptera, 81.
numismatis, 20.
operatola, xiv.
operator, xiv.
quadrilineatus, 91.
quercus baccarum, 15.
quercus folii, 60.
quercus ramuli, 59.
radicis, 28.
scutellaris, 60.
seminationis, 87.
Sieboldi, 34.
spongifica, 2.
tinctoria, 165.

Darwin, C, xxiii, xxxii, xxxviii.
Decatoma biguttata, 15, 47, 63,
69, 79.

immaculata, 77, 79.

Neesi, 44, 47, 60.

signata, 79.
Dendrocerus Lichtensteinii, 79.
Derham, Dr., xi, xxxviii, 166.
Determinants, xxiii.
Devonshire gall, The, 163.
Diastrophus glechomae, 159.

rubi, 159.
Dictyopteryx Loeflingiana, 60.

Dimorphism, xiv, 3, 5.
Diplolepis, xii.

scutellaris, 60.
Diptera, 78.

Dromius quadrimaculatus, 77-
Drosophila, 77.
Dryophanta, 8, 60, 134.

divisa, xxxiii, 67, 69, 95, 145.

longiventris, xxxiii, xl, 64,
66, 95.

scutellaris, xxxiii, 60, 64, 65,

68, 82, 95.
verrucosus, 69.

Dryoteras, 71.

Echinus microtuberculatus, xxii.
Egg, development of, 14, 144.

lailure, 13, 107.

rest, II, 14, 144.
Eggs, number of, xxix, 32, 72.

situation of, xxxiv, 102, 108.
Egg-stalk, 115, 122.

function of, 124, 127.
Elachestus cyniphidinm, 66, 79.

petrolatus, 47.
Embryo, development of,i 25,127.
Entedon amethystinus, 79.

cecidomycarnus, 47.

deplanatus, 79.

flavomaculata, 15.

leptoneurus, 50.

scianeurus, 47, 79.
Eulophus agathyllus, 79.

gallarum, 77.

laevissimus, 47.

metallicus, 47.

ramicornis, 79.
Eupelmus annulatus, 18, 47.

azureus, 42, 79.

urozonus, 21, 69.
Eurytoma gracilis, 47.

nodularis, 63.

rosae, 18, 30, 35, 42, 47, 63,

69, 79. 85. 89-
semirufa, 60.
setigera, 63, 69.
signata, 15, 50, 69.
squama, 69.
verticillata, 46,

Fabricius, xi.

194

Index.

Fecundation, 32.

Fitch, E. A., xiv.

Fletcher, J. E., 21.

Forster, xiii.

Fol, on polar cells, xxviii.

Food of Cynipidae, 137, 140.

Forficula auricularia, 77.

Frank, xiv.

Furrowed catkin gall. The, 93.

Gall, aborted, 107.

dwellers, xii.

evolution, xxxii.

flies, breeding of, 5, 9.

formation, beginnings of, 14,
17, 20, 29, 32, 97, 136.

exciting causes of, xxxviii.

seats of, xxxiv.
Galls, classification of, xxxiii.

compound, 33.

defensive characters of, xxxvi.

duration of life of, xxxix, 19.

superimposed, 105.
Ganglion, abdominal, 114, 120.
Geddes and Thomson on polar

cells, xxvii.
Gemmules, xxiii.
Generation cycles, xvi.
Geniocerus cyniphidium, 66, 79.
Geoffroy St. Hilaire, xii.
Germogen, xxx.
Germ-plasm, alternating, xxxi.

continuity of, xvi.

tracts, xxvii.
Giraud, xiii, 52.
Glands, vaginal accessory, 143.
Globular gall, The, 42.
Green velvet bud gall, The, 67.
Guest-flies, xii.

Haeckel, xxiii.
Hairy catkin gall, The, 52.
Hairy pea gall. The, 25.
Hartig, T. von, xii, i, 115.
Hartog, Prof. M., xxvi.
Hemiptera, 78; polar cells in, xxx.
Hemiteles areator, 77.

coactus, 79.

punctatus, 79.
Hertwig, 0.,on polar cells, xxvii.
Heterogenesis, 149.

Homalomyia canicularis, 60.
Hop gall. The, 50.
Hydroids, xv.
Hymeuoptera, 78.

Ichnenmonidae, 126.
Idants, xxiii.
Ids, xxiii.

Inostemma Boscii, 77.
Inquilines in galls, xii, 15, 106.

eggs of, 127.
Intestinal systemofCynipidae, 1 38.

Kidney gall, The, 81.
Knot gall. The, 34.
Kraepelin, no, 113.
Kupffer, xxx.

Lacaze-Duthiers, xiii, xxiii.
Lammas shoots, 25, 34.
Lampronota segmentata, 79-
Larva, development of, 147.

influence of, 100, 104.
Larval states, xvii, 143.
Latreille, xii.
Latridius lardarius, 77.

trans versus, 78.
Lepidoptera, 78.
Leptoptera appendiculata, xvi.
Leuckart, xvii.
Leydig, 139.
Lichtenstein, J., xiii, xvii, 114,

143, 150.
Life, duration of, in Cynipidae,

140.
Limneria exareolata, 84.
Linnaeus, xi.
Liodora, 60.
Liver-flukes, xvi.
Lozotaenia xylosteana, 77.
Lubbock, Sir J., 99, 149.

Macrocentrus marginator, 167.
Males absent, xviii.
functionless, xiii.
Malpighi, Marcellus, xi, xxxviii,

52-
Malpighian tubes, 139.
Malpighi"s gall, 56.
Manderstjernia, 9, 143.
Maple gall, The, 159.

Index.

195

Mathiolus, xi.

Mayr, Prof. G., xiii, 159-162.
Medusae, xvi.

Megastigmus Bohemanni, 78.
dorsalis, 15, 34, 37, 42, 44,

50, 59. 63, 77. 78-
stigmaticus, 167.
xanthopj'gus, 78.
Mesopolobus fasciiventris, 47,

50, 79, 81.
Metagenesis, xiv, 149.
Metempsychosis, x.
Metenteron, 13S.
Meteorological conditions, effects

of, 14.
Methods, experimental, 7, 10.
Microdus rufipes, 79.
Microgaster, 77.
Microtypus Wesmaelii, 79.
Minot, C. S., xxvii.
Mivart, St. George, on natural

selection, xxxv.
Mouth, parts of, 137.
Muscles, 111.

Natural selection, influence on

gall-flies, xxxiv.
Nematus Vallisnierii, 99, 150.

ventricosus, 150.
Neuroptera, 78.
Neuroterus, 8, 9, 130, 146.
albipes, 19.
Aprilinus, 85.
baccarum, 15.
farunculus, 85.
fumipennis, xxxiii, 18, 22,

23, 24, 27, 95, 123, 131.
laeviusculus, xxxiii, 18, 19,
20, 23, 25, 95, 101, 113,
114, 116, 131.
lenticularis, xviii, xxxi, xxxiii,

4, 5, 9. ".13. 15. 17, 21,

22, 23. 25, 95.
Malpighii, 9.
nnmismatis, xxxiii, 20, 21,

22, 25, 95.
ostreus, xxxiii, xxxviii, xl,

84. 85, 95.
parasiticus, 42, 63,
pezizaeformis, 18.
Reaumuri, 20.

Neuroterus tricolor, 24.

vesicatrix, 21.
Nitidula grisea, 77.
Noctua, 77.
Nucleus, changes in, xx.

Oak-apple, 77.
Oblong plate, The, in.
Odours, defensive, xxxvii.
Olinx debilis, 60.

euedoreschus, 79.

gallarum, 60.

scianeurus, 47, 79.

trilineata, 35, 50, 91, 93.
Olivier, xii.
Oozoon, xxvii.
Orchestes quercus, 77.
Orthoptera, 78.
Orthostigma gallarum, 63.
Osten-Sacken, Baron C. R., xiii,

2.
Ovaries, 141.
Oviposition, 12, 72, 82, 115,

117, 118.
Ovipositor, 26, 27, 130, 132.
Owen, R., xv.
Oyster-gall, The, 85.

Paget, Sir James, on galls, xxxviii.
Palpi, 27, 138.

Pangenes, of De Vries, xxii,xxiii.
Parasites, xii, 15.
Parthenogenesis, i, 3, 150.

evolution of, 154.

in Saw-flies, 151.

male, xx, xxii.

value of, xix.
Pediaspis aceris, 159.

sorbi, 159.
Penis, 142.

Pentatoma lurida, 77.
Pezomachus gallarum, 15.
Pheasants, xxxvi.
Phylloxeridae, xviii.
Physoevria, 77.
Pimpla alternans, 79.

calobata, 79.

caudata, 79.
Pimplidae, 77, 122.
Pink wax gall, The, 84.
Plastidules, xxiii.

0 2

196

Index.

Pleurotropis cyniphidium, 81.
Pliny on galls, x.
Polar cells, xx.

fertilization of, xxvii, xxx.

function of, xxiv.

of parthenogenetic egg, xx,
xxix.

of sexual eggs, xxix.

retained, xxxi.
Polyspermy, xxx.
Porizon claviventris, 63.
Primitive germ-cell, xxi, xxii.

sperm-cell, xxi, xxii.
Protective characters, xxxiii, 104.
Psocus subocellatus, 77.
Pteromalus bisignatus, 85.

cordairii, 47, 79.

decidens, 78.

dilectus, 77-

dubius, 78.

Dufourii, 79.

fasciculatus, 63.

fasciiventris, 77.

fuscipennis, 77.

gallicus, 79.

hilaris, 77.

incrassatus, 69.

jucundus, 47, 63.

leucopezus, 79.

meconatus, 47, 79.

naubolus, 77.

ovatus, 77.

planus, 78.

platynotus, 78.

puparum, 151.

Ratzeburgi, 60.

Saxescenii, 47, 69, Si.

semifascia, 77.

stenonotus, 79.
Purple velvet bud gall. The, 64.

Quercus bicolor, 3.

pedunculata, 15,50, 172.
pubescens, 15, 172.
sessiliflora, 7, 15, 50, 172.

Radoszkowsky, 9, 143.
Ratzeburg, xiii.
Reaumur, xii, xxxviii.
Receptaculum seminis, 16, 32,
142.

Rectal, papilla, 132.

glands, 139.
Rectum, 132.

Red barnacle gall, The, 35.
Red wart gall, The, 70.
Reinhard, xiii, 3.
Reproductive rudiment, xxx.
Respiratory organ, Eggstalk as,

124.
Rhodites eglanteriae, 143, 152,

159-

rosae, xvii, 143, 152, 159.

spinosissima, 159.
Riley, xiii.
Rolph, 153.

Romanes, Prof., on galls, xxxii.
Root gall. The, 73.
Roots, how pricked, 32.
Rosechafers, 77-
Rotifera, 153.

Salix amygdalina, 99, 150.

Salpae, xii.

Sapholytus connatus, 34, 44,

63.

Scarlet pea gall. The, 69.
Schenck, xiii.
Schenck's gall, 20.
Schlechtendal, xiii.
Seta, no.

Sex, differentiated in G^g'g, 77.
Sexes, order of appearance, 16.
Sexual reproduction, xviii.

rudiment, xxv.
Siebold, Prof, v., 150.
Siphonura brevicauda, 54.

chalybea, 42.

viridiana, 47.
Spangle gall. The common, 15.

The cupped, 24.

The silk-button, 21.

The smooth, 19.
Spathegaster, 9, 130, 146.

albipes, xxxiii, xxxix, 19, 47>

9.'^. 131-
Aprilinus, xxxiii, 85, 86, 95.
baccarum, xviii, xxxi, xxxiii,

xxxix, 5, 13, 15, 17, 24,

95-100.
interruptor, 15.
similis, xxxix, 66, 67, 86, 95.

Index.

197

Spathegaster, Taschenbergi,

xxxix, 62-67, §2, 86, 95,

134-
tricolor, xxxix, 24, 27, 95.
varius, 22.

vesicatrix, xl, 21, 95.
verrucosus, xxxix, 69, 70, 95,

145-
Species, fixity of, xxxii.
Spencer, Herbert, xxiii.
Spermatogenesis, xxi.
Sphaerechinus granulans, xxii.
Spiculae, 110.
Spotted bud gall, The, 94.
Squirrels, xxxix.
Stalivcd spindle gall. The, 54.
Steenstrup, xv.
Stomach, 138.
Sycamore gall. The, 161.
Symbiosis, xii.
Synergus, xii, 22, 25.

albipes, 17, 25, 59, 69, 89.

apicalis, 17, 20, 34, 37, 47,
50, 66.

erythrocerus, 84.

evanescens, 50.

facialis, 17, 25, 47, 60, 78,
84, 89, 93, 94, 167.

incrassatus, 30, 35, 39.

melanopus, 50, 167.

nervosus, 42, 46, 54, 59.

palliceps, 46.

pallicomis, 63, 66, 69, 81,
84, 107.

radiatus, 17, 47, 60, 94.

Reinhardi, 167.

ruficornis, 17, 42, 59, 81.

socialis, 77.

Thaumacera, 17, 25, 47, 81,
84.

tibialis, 81.

tristis, 85.

Tscheki, 15, 19, 21, 24, 63,
69, 85.

variolosus, 59.

varius, 81.

vulgaris, 34, 42, 50, 54, 63,
81.
Synoptical table of galls, 168.
Syntomaspis caudata, 15, 46, 50,
78.

Syntomaspis crinicaulis, 78.
cyanea, 66, 69.
dubius, 47.
fastuosa, 15, 84.
lazulina, 63, 66, 69.

Taschenberg, xiii.
Telenomus phalaenarum, 47.
Temperature affecting gall-flies,

141.
Teras amentorum, 59.

terminalis, xxxiii, 73, 74, 75,

76, 95, 134-
Terebra, no,

tactile hairs of, 1 19.
Tetrastichus atrocaeruleus, 18.

diaphantes, 77.

quercus, 30.
Thrips, 78.
Tit-mice, xxxvii.
Tortrix, 18, 77.

Torymus abdominalis, 18, 47,
63, 66, 69, 77, 78-

admirabilis, 79.

amoenus, 30, 84.

appropinquans, 78.

auratus, 15, 18, 44, 47, 60,

78, 93-
autumnalis, 78.
cingulatus, 78.
confinis, 78.
corticis, 39.
cyniphidum, 78.
elegans, 63.
erucarum, 30.
flavipes, 84.
fuscicrux, 21.
geranii, 21.
hibernans, 15, 19.
inceitus, 18, 63, 79.
inconstans, 21, 50, 77, 78.
leptocerus, 78.
leucopterus, 78.
longicaudis, 78.
minutus, 78.
muscarum, 78.
mutabilis, 21, 77, 78.
nanus, 78.
nobilis, 30, 35, 73.
propinquus, 78.
pubescens, 69.

198

Index.

Torymus, radicis, 30.

regius, 18, 42, 50, 63, 66,6^,
78, 167.

nibripes, 94.

social is, 19, 24.

viridissimus, 78.
Trematoda, xvi.

Trigonaspis crustalis, xxiv,
xxxvii, xxxix, 64, 80, 81,
82, 95, 100, 138, 144.

megaptera, 79, 81 •

renum, 79.
Truffle gall, The, 30.
Tryphon, 123.
Tufted gall, The, 55.
Twig gall. The, 44.

Units, physiological, xxiii.

Vagina, 141, 143.
Vein gall, The, 37.
de Vries on potentialities of
growth, XXXV.

Wachtl, xiii.
Walker, F., xiv, 77.
Walsh, xiii, 2, 3, 4, 5.
Wallace, A. R., 3.
Weismann, A., xx, xxiii, xxiv.
Westwood, xiv.
Wings, rudimentary, 76.
Winter buds, 107.
Wintering galls, 10.
Woolly gall, The, 60.

Zeiraphera communana, 18, 78.

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