SCALE OF SEXES
Asexual reproduction.--Formation of the animal colony.
--Limits of asexual reproduction.--Coupling.--Birth of
the sexes.--Hermaphrodism and parthenogenesis.--Chemical
fecundation.--Universality of parthenogenesis.
The primitive mode of reproduction is asexual, or what one will so
consider provisorily, in comparison with more complex mechanism. In the
first living forms there are neither sexual organs nor differentiated
sexual elements. The animal reproduces itself by scissiparity or by
budding; the individual divides itself in two parts, or a protuberance
develops, forms a new being and then separates.
Scissiparity is an inexact term, for the division is transversal, and
the two parts far from equal; it occurs in protozoaires, and further
in worms, star-fish and polyps. Budding is common to protozoaires,
infusoria, cœlenterata, to fresh-water polyps and to nearly all
vegetables. A third primitive mode, sporulation, consists in the
production inside the organism of particular cells, spores, which
separate and become individuals; this occurs in protozoaires, as well
as in ferns, algæ and mushrooms.
The first two modes, division and budding, serve also for the formation
of animal colonies, when the new individual retains a point of contact
with the generating individual. It is by this notion of colony that
one explains complex beings, and even superior animals, in considering
them as reunions of simple primitive beings which have differentiated
themselves and still retained a solidarity, sharing the physiological
work between them. Colonies of protozoaires are formed of individuals
having identical functions, living in perfect equality, despite
the hierarchy of position; colonies of metazoaires are composed of
specialised members whose separation may be a cause of death for the
total individual. There is then, in the latter case, a new being
composed of distinct elements which, retaining a certain essential
autonomy, have become the organs of a new entity.
The first living organisms formed their hierarchies thus: individual
unicellular, or plastide; group of plastides or meride. The merides,
as the protozoaires, can reproduce themselves asexually, or by
division or budding. They may separate completely or remain attached
to their generator. If they remain attached one has mounted a step and
attained the zoide. Thence, by colonies of zoides one gets individuals
still more complex, called demes. None of these terms is much more
than a convenience for memory. The nomenclature stops, as does the
progression, at a certain moment, for the evolution has its limit, its
finality, as does even the milieu in which life continues to evolve.
One might say that heaving up from the obscure vital centre, the new
animal-shoots branch upward until they knock their heads upon an ideal
or imaginary roof which prevents any further climbing. This is the
death of the species, and Nature contemptuously abandoning her work,
begins to mate yet another mould of the initial ooze, to derive from
it a new form. The dream of an unlimited transformation of actual
species is pure chimæra; they will disappear one by one, according to
their order of primogeniture, according to their faculty for adapting
themselves to the changing milieu, and one might foresee, if the earth
lasts, in a distant time an unimaginable fauna replacing the present
fauna, and even replacing man.
Man is a metazoaire, that is to say an animal with differentiated
pluricellules, like the sponge, the wheel animals, and the annelids.
He belongs to the artizoaire series: a head, belly, back, bilateral
symmetry; to the vertebrate branch: internal skeleton, cartilaginous
and osseous; to the class of mammifers, to the sub-class of
placentaires; to the group of primates not far from the chiroptera
(bats) and the rodents.
In regard to the life-transmitting mechanism the animals are
divided somewhat differently. On one side budding and division, or
scissiparity, is prolonged rather far into the metazoaire series
concurrent with sexual reproduction; on the other hand there are, among
protozoaires, phenomena of coupling, unions of cellules which resemble
veritable fecundation and perform its rôle; without the nuclear
regeneration which is the aim and consequence, neither segmentation
nor budding can take place, at least not indefinitely. In sum, the
reproduction of beings is always sexual; only in the one case, the
protozoaires, it is produced by non-differentiated elements; and in
the other, the metazoaires, by differentiated elements, a male and a
female. If one clips off bits of a sponge, a hydra, one obtains as many
new individuals, which when they have grown one may again divide, and
so on repeatedly, but not indefinitely. At a variable instant, after
a certain number of generations by fragmentation, senescence appears
among the so produced individuals; the clipped morsels remain inert.
Thus this sort of artificial virgin birth has a limit, as has normal
parthenogenesis, and in order that the individuals may regain their
parthenogenetic force one must give them time to regenerate their
cellules by the coupling which fecundates them.
Fecundation is in all cases, doubtless, merely a rejuvenation, thus
considered it is uniform not only throughout the animal series, but
throughout the vegetable. One ought to experiment in slip-cutting, and
discover at what point the slip cut from a slip begins to diminish
in vitality. Coupling and fecundation have the same result: it is
necessary that cellules A unite with cellules B (macro-nucleus and
micro-nucleus among protozoaires; ovule and spermatozoid among
metazoaires), in order that the organism may usefully exteriorize a
part of its substance. When the too complex organism has lost the
primitive faculty of segmentation, it makes use, directly, to reproduce
itself, of certain cellules differentiated for that purpose: it is
these cellules united into a whole, which reintegrate and give birth to
a double of the generating individual or individuals. From the top to
the bottom of the sexual scale the new being springs invariably from
a duality. The multiplication takes place only in space. In time the
product is a contraction, two giving one.
Scissiparity is compatible with the existence of separate sexes, as in
the starfish. This fantastic animal with no instrument save its suckers
opens oysters, envelops them with its stomach which it unbellies
(vomits), devours them. It is not less curious in reason of its variety
of reproductive mode, serving itself of sexual apparatus, or budding,
or casting an arm which becomes a new creature. Thus it is difficult to
class animals according to their manner of reproduction; hermaphrodism
is another block. This mode is doubtless primitive, since it is of
the type of protozoaire coupling, but it is greatly complicated when
it persists, for example up to the moment where it disappears in the
mollusk series, whereof some possess so luxurious a love-organism. The
simple and very naive form, that in which the sperm and the eggs are
produced simultaneously inside the same individual, is found only in
inferior organisms. Normal parthenogenesis belong equally to summary
and to complicated animals, to wheel-animals and to bees. Among
arthropodes, that is to say among insects in general, the sexes are
always separate, save in certain tardigrade arachnids, but these are
the ones which offer the finest cases of parthenogenesis, generation
without aid of the male. The term need not be taken literally. For
as there is no indefinite scissiparity without coupling, there is no
unlimited parthenogenesis without fecundation: the female is fecundated
for several generations which transmit this power, but there comes
a day when the female who has not encountered a male gives birth to
males and females. They couple and produce females parthenogenetically
endowed. This has been for long time a mystery,--it is still a mystery,
for side by side with normal parthenogenesis there is irregular
parthenogenesis, there are cases where non-fecundated eggs behave
exactly as fecundated eggs, without anyone's knowing why.
The virgin-begotten cycle of plant-lice is famous, that of
wheel-animals not less entertaining. The males, smaller than the
females, live but two or three days, couple and die. The fecundated
females lay eggs whence come nothing but females, unless the eggs are
subjected to a temperature above 18 degrees (centigrade); above that
the eggs hatch out males. Between the periods of coupling there are
long stretches of virgin-birth, nothing but females producing females,
until the temperature permits a male hatch. In two years the plant
louse runs through ten or twelve parthenogeneses; in July of the second
year, there appear winged individuals, these are still female, but
double size, and they lay two sets of eggs, whereof the smaller hatch
male (the male is three or four times smaller than the female), the
larger eggs hatch female; there is coupling and the cycle begins again.
For long people believed the plant louse truly androgynous. Réaumur
and Bonnet, having seen isolated plant-lice reproduce themselves were
convinced of this, when Trembley, a man of genius, celebrated also for
his observations of hydra, threw out the idea: Who knows whether a
coupling of these lice does not fecundate them for several generations?
He had discovered the basis of parthenogenesis. Facts upheld him.
Bonnet described the male and female, and noted even the genital ardour
of this sticking leaf-louse, this milch-cow of the ants.
Parthenogenesis is a sign-post. Nothing more clearly demonstrates the
importance of the male or the precision of his function. The female
appears to be the whole show, without the male she is nothing. She
is the machine and has to be wound up to go. The male is merely the
key. People have tried to obtain fecundation by false keys. Eggs of
sea-anemones, and star-fish have been hatched by contact with exciting
chemicals, acids, alkalines, sugar, salt, alcohol, ether, chloroform,
strychnine gas, carbonic acid. But one has never been able to bring
these scientific larvæ to maturity, and everything leads one to believe
that if one succeeded, and that if these artificial beings were
capable of reproduction, it would be but for a limited period. This
provoked parthenogenesis is neither more nor less interesting than
the normal. It is doubtless abnormal, but abnormal parthenogenesis
is not infrequent in nature; eggs of the bombyx, of star-fish, and
of frogs, hatch sometimes without fecundation, and very probably
because they have accidentally come up against the very stimulant
which the excellent experimenters have lavished on them. Whether
sperm acts as an "excitant" or as fecundator, the action is no easier
to understand by one label than by another. The queen bee lays both
fecundated and non-fecundated eggs; the first hatch female, the second
invariably male, here the male element would seem to be the product
of parthenogenesis and the female to require previous fecundation. In
contrast, among plant-lice, the generations of female continue for
nearly two years. There is an order in these things, as in all things,
but it is not yet apparent; one notes only, that however long and
varied be the parthenogenetic period, it is limited somewhere by the
necessity of the female principle being united with the male principle.
After all, hereditary fecundation is no more extraordinary than
particular fecundation, it is a mode of perpetuating life which the
exercise of one's reason should make one consider as perfectly normal.
One ought, at the end of this summary chapter, to be courageous enough
to say that fecundation, as vulgarly understood, is merely an illusion.
Taking man and woman (or no matter what dioic metazoaire) the man
does not fecundate the woman; what happens is at once more mysterious
and more simple. From the male A, the great Male, and from the great
Female B are born without any fecundation whatever, spontaneously,
little males a and little females 6. These little males are called
spermatozoides, and the little females, ovules; it is between these new
creatures, between these spores, that the fecundating union occurs. One
then observes that _a_ and _b_ resolve themselves into a third animal
_x_, which by natural growth becomes either A or B. Then the cycle
begins again. The union between A and B is merely a preparation; A and
B are nothing but channels carrying _a_ and _b_, carrying them often
far beyond themselves. Like the plant-lice or drones, the mammifers
called man are subject to alternate generation, one parthenogenesis
always separating the veritable conjunction of the differentiated
elements. Coupling is not fecundation; it is merely the mechanism; its
utility is merely in that it puts two parthenogenetic products into
relation. This relation occurs inside the female, or outside the female
(as in case of fishes); the milieu has an importance of fact, not of
principle.