Origin of Species Variorum

→ Sometimes 1869 1872

In some cases 1866

→ then through the 1869 1872

through the 1866

→ crustaceans would have appeared as nauplii, if there 1866 1869

OMIT 1872

→ development. 1869

development;— or that they were primordially developed under this form. 1866

development, all these crustaceans would have appeared as nauplii. 1872

→ the general, 1869

of embryos of different species within the same class, generally, 1859 1860 1861 1866

the common, 1872

→ between the embryos or larvæ 1869 1872

each other;— 1859 1860 1861 1866

→ most distinct species in the same class;— 1869 1872

structure of 1859 1860 1861 1866

→ retaining whilst within the egg or womb, structures which are of no service to it, either at that period or later in life; whilst embryos at a later period, or larvæ, which have 1869

not being closely related to its conditions of existence, except when the embryo becomes at any period of life active and has 1859 1860 1861

not being closely related to its conditions of existence, existence, except when the embryo becomes at any period of life active and has 1866

often retaining whilst within the egg or womb, structures which are of no service to it, either at that or at a later period of life; on the other hand larvæ, which have 1872

→ their own wants, are perfectly adapted to the surrounding conditions;— and lastly the fact of certain larvæ standing higher in the scale of 1869

itself;— of the embryo apparently having sometimes a higher 1859 1860 1861 1866

their own wants, being perfectly adapted to the surrounding conditions;— and lastly the fact of certain larvæ standing higher in the scale of 1872

we see

hardly any

trace of the vermiform stage.

→Sometimes it is only the earlier developmental stages which

fail;

these

apparently

having

been

suppressed.

Thus Fritz

Müller

has

recently

....

made the remarkable discovery that certain shrimp-like crustaceans (allied to Penœus) first appear under the simple nauplius-form, and

passing

after passing

through two or more zoea-stages, and →then through the mysis-stage, finally acquire their mature structure: now in the whole

enormous

great

malacostracan

order,

class,

to which these crustaceans belong, no other member is as yet known to be first developed under the nauplius-form, though

very

....

many appear as zoeas; nevertheless

Müller

assigns reasons for his

belief,

belief

that

all

there

these

→crustaceans would have appeared as nauplii, if there had been no suppression of →development.

How, then, can we explain these several facts in embryology,—

namely

namely,

the very general,

but

though

not

universal

universal,

difference in structure between the embryo and the adult;—

the various

parts in the same

indivividual

individual

embryo

embryo,

which ultimately become very unlike and serve for diverse purposes, being at

this

early period of growth alike;— →the general, but not

universally,

invariable,

resembling

resemblance

→between the embryos or larvæ of the →most distinct species in the same class;— the embryo →retaining whilst within the egg or womb, structures which are of no service to it, either at that period or later in life; whilst embryos at a later period, or larvæ, which have to provide for →their own wants, are perfectly adapted to the surrounding conditions;— and lastly the fact of certain larvæ standing higher in the scale of organisation than the mature

animal,

animal

animals

into which

it is

they are

developed.

developed?

I believe that all these facts can be

ex- plained,

explained,

follows,