TRANSACTIONS OF SECTION D, 761 
eéming into contact and fusing. The same may be said with regard to the 
so-called sexual differences of the parents of the two kinds of gametes, and to the 
powerful instincts which regulate their action. The conjugation of the male and 
female gamete, or the fertilisation of the ovum, as it is sometimes called, consists 
in the fusion of two distinct masses of protoplasm which are nearly always produced 
by different individuals, In the case of hermaphrodites, the term applied to 
organisms which produce both male and female gametes in the same individual, 
there is generally some arrangement which tends to prevent the male gamete from 
conjugating with the female gamete of the same parent; but this phenomenon is 
not absolutely excluded, and takes place as a normal phenomenon in many plants 
and possibly in some animals, 
This fusion of the protoplasm of the two gametes gives us a uninucleated 
organism— for the fusion of the nuclei of the two gametes seems to be an essential 
part of the process—in which the potencies of the two gametes are blended. The 
sygote, as the mass formed of the fused gametes is called, is formed by the com- 
bination of two individualities, and is therefore essentially a new individuality, the 
characters of which will be different from the characters’ of both of the parents. 
This fact, which is not apparent in the zygote when first established, because the 
parts are hardly distinguishable by our senses, becomes obvious as soon as organs, 
with the appearance of which we are familiar, are formed. As a general rule this 
cannot be said to have occurred until what we call maturity has been nearly 
reached, because we are not familiar enough with the features of immature organ- 
isms to detect individual differences. But you may rest assured that such differ- 
ences exist at all stages of growth from that of the uninucleated zygote till death. 
How the characters of the two parents will combine in the zygote it is impossible 
to predict, and the result is never the same even though the conjugations have 
been between gametes of identical origin. There may be an almost perfect 
mixture, the blending extending to even quite minute details; or the characters 
of the one parent may predominate—be prepotent, as we call it—over those of 
the other; or they may blend in such a way that the zygote offers characters found 
in neither parent. Or, finally, the features of one parent may come out at one 
stage of growth, those of the other at another stage. But, however the characters 
muy blend, the product never exactly resembles the parents. The extent to which 
it differs from them is the measure of the variation. 
To resume, it will be observed that in the method of reproduction sometiines 
called sexual, two distinct processes occur. One of these is the real reproductive 
act, which consists in the production by fission of uninuclear individuals called 
gametes; the second is the fusion of the gametes to form the zygote. The gametes 
are of two kinds, and the reason of there being two kinds is intelligible when we 
consider the parts they have to play. The male gamete is nearly always endowed 
with locomotive power, and the female gamete is stored with food material to be 
used by the zygote in the first stages of growth. The destiny of these two uninu- 
cleated organisms is to fuse with one another, and so to give rise to a zygote 
which ultimately assumes the typical form of the species. Asa general rule the 
gametes have but a limited duration! of life unless they conjugate, and this is 
quite intelligible when we remember that they have no organs, eg. digestive 
organs, suitable for the maintenance of life. It is rarely found that they have the 
power of assuming the form of their parent, unless they conjugate. This never 
happens in the case of the male gamete (at any rate in animals), and only rarely 
in that of the female. When it occurs—that is to say, when the ovum develops 
without conjugation—we call the phenomenon parthenogenesis. Parthenogenesis 
is found more commonly in Arthropods than in other groups, but it may be more 
common than is supposed.? 
‘ Under favourable conditions they may live a considerable time—e.g. the sper- 
matozoon of certain ants, which are stated by Sir John Lubbock to live in some cases 
for seven years. 
? It may be mentioned as a curious fact that parthenogenesis is rarely found in 
the higher plants, and, as I have said, is not known for the male gamete among 
animals. 
