Essays Upon Heredity and Kindred Biological Problems: Authorised TranslationWeismann, August
Science
Essays Upon Heredity and Kindred Biological Problems: Authorised Translation
Weismann, August
Evolution (Biology); Genetics; Reproduction
The correctness of this explanation is shown by a consideration of the
males and the second form of females; for in these cases the body falls
to pieces, not as a consequence of reproduction, but as a preparation
for it!
Götte only mentions the second female form in a note, in which he says,
it appears ‘that in the second female form of these animals the whole
body breaks into many pieces, and the superficial layer gradually
atrophies, so that it dies before the eggs are extruded.’ In Julin’s
account[76], upon which Götte bases his statements, there are, however,
some not unimportant differences. For instance, the eggs are not
extruded at all, but embryonic development takes place within the body
of the mother, which has previously undergone spontaneous division into
several pieces. In this case, the eggs differ from those of the other
female form, inasmuch as they do not constitute the whole of the
endoderm, but are embedded (as was stated above) in a fairly voluminous
granular mass at the expense of which, or at least by means of which,
they are nourished; for they increase considerably in size during their
development. But not only this granular mass, but all the layers of the
body of the mother, even the ectoderm, persist during the embryonic
development of the offspring. Indeed, the ectoderm must continue to
grow during the division of the mother animal, for it gradually covers
in the products of division on all sides, and, by means of its cilia,
causes the animal to swim about in the fluids of its host. After some
time the cilia are lost, and the separate parts into which the mother
animal has divided, fix themselves upon some part of the body-cavity of
the host; the young become free, and the remains of the body of the
mother probably disappear by dissolution and resorption[77]. In this
case the remains of the mother animal seem to be, to some extent,
consumed by the embryos,—a process which sometimes, although very
rarely, happens elsewhere. We can scarcely consider this as a primitive
arrangement, or look upon it as a proof that ‘reproduction’ has a
necessarily fatal effect upon the Polyplastid organism.
In the male, the mass of spermatozoa does not swell out the body to
such an extent that its walls must give way and thus permit an exit,
but the large ectoderm cells atrophy spontaneously at the time of
maturity, and as they fall off, exit is given to the spermatozoa here
and there. In this instance also the dissolution of the body is not a
consequence of reproduction, but reproduction can only take place when
the dissolution of the body has preceded it!
In this remarkable arrangement we cannot discern anything except an
evident adaptation of the life of the body-cells to reproductive
purposes, and this adaptation was rendered possible because, after the
evacuation of the sexual cells, the body ceased to be of any value for
the maintenance of the species.
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