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EMBRYOLOGY. 539
The intercellular substance is broken up into fibres, both yellow and
white. The yellow fibres are ela>iiic (Fig. 278), and are more or less
abundant in areolar tissue. The Nvliite fibres form the interlacing net-
work which binds the tissues together throughout the body. They are
joined in bundles, as may be seen by referring to Fig. 277.
There yet remains to be considered hyaline cartilage, which belongs
to the connective-tissue group. In this tissue spheroidal flattened or
angular cells, containing one or more nuclei, are seen lying in a homo-
geneous basement-substance (see Fig. 279), which is said to yield chon-
drin upon being boiled. The cells are sometimes finely, at other times
coarsely, granular. Both the capsule which surrounds the cell and the
hyaline intercellular substance possess higher refractive power than does
the cell itself.
Having thus brought our brief examination of a few of the more
important characteristics of cell-action and morphology to a close, it
only remains to express the hope that it will stimulate the student to
a better and more careful survey of the whole subject. The import-
ance of such a survey cannot be too strongly urged upon his attention,
for without definite knowledge of cellular structure it is impossible to
prosecute histological inquiries with any degree of success.
We are now better able to enter upon the subject of Embryology, a
subject in regard to which what we know at present is so little in com-
parison to what we do not know that there remains an illimitable field
for our inquiries and discoveries.
Embryology.
Down to our own century, though many important truths bearing
upon embryology were known to anatomists and physiologists, nothing
could have been farther from their conception than the fact now uni-
versally admitted that all animals, without exception, arise from eggs.
Aristotle and his followers recognized three modes of generation
viz. oviparous, viviparous, and spontaneous generation. By the prog-
ress of investigation the last mode of generation was shown to be a
thing unknown in Nature, and in 1651, Dr. William Harvey announced
that there is no essential difference in the mode of generation between
oviparous and viviparous animals, but that "all animals whatsoever,
even the viviparous, and man himself not excepted, are produced
from ova." A little later Linnteus expressed this great truth in the
sentence so often quoted, " Omne vivum ex ovo ;" but neither he nor
Harvey appreciated the full significance of these statements, for the exist-
ence of the mammalian e^g was not then dreamed of. Since then the
discoveries of Von Baer, Negrier, Pouchet, and others have shown not
only that " the egg is common to all living beings without exception,
from the lowest radiate to the highest vertebrate, but that its structure
is at first identical in all, composed of the same primitive elements and
undergoing exactly the same process of growth up to the time when it
assumes the special character peculiar to its kind ;" and the only real
diiference between oviparous and viviparous animals is that in the Ovip-
ara the fecundated egg is discharged from the body of the female and
EMBRYOLOGY. 539
The intercellular substance is broken up into fibres, both yellow and
white. The yellow fibres are ela>iiic (Fig. 278), and are more or less
abundant in areolar tissue. The Nvliite fibres form the interlacing net-
work which binds the tissues together throughout the body. They are
joined in bundles, as may be seen by referring to Fig. 277.
There yet remains to be considered hyaline cartilage, which belongs
to the connective-tissue group. In this tissue spheroidal flattened or
angular cells, containing one or more nuclei, are seen lying in a homo-
geneous basement-substance (see Fig. 279), which is said to yield chon-
drin upon being boiled. The cells are sometimes finely, at other times
coarsely, granular. Both the capsule which surrounds the cell and the
hyaline intercellular substance possess higher refractive power than does
the cell itself.
Having thus brought our brief examination of a few of the more
important characteristics of cell-action and morphology to a close, it
only remains to express the hope that it will stimulate the student to
a better and more careful survey of the whole subject. The import-
ance of such a survey cannot be too strongly urged upon his attention,
for without definite knowledge of cellular structure it is impossible to
prosecute histological inquiries with any degree of success.
We are now better able to enter upon the subject of Embryology, a
subject in regard to which what we know at present is so little in com-
parison to what we do not know that there remains an illimitable field
for our inquiries and discoveries.
Embryology.
Down to our own century, though many important truths bearing
upon embryology were known to anatomists and physiologists, nothing
could have been farther from their conception than the fact now uni-
versally admitted that all animals, without exception, arise from eggs.
Aristotle and his followers recognized three modes of generation
viz. oviparous, viviparous, and spontaneous generation. By the prog-
ress of investigation the last mode of generation was shown to be a
thing unknown in Nature, and in 1651, Dr. William Harvey announced
that there is no essential difference in the mode of generation between
oviparous and viviparous animals, but that "all animals whatsoever,
even the viviparous, and man himself not excepted, are produced
from ova." A little later Linnteus expressed this great truth in the
sentence so often quoted, " Omne vivum ex ovo ;" but neither he nor
Harvey appreciated the full significance of these statements, for the exist-
ence of the mammalian e^g was not then dreamed of. Since then the
discoveries of Von Baer, Negrier, Pouchet, and others have shown not
only that " the egg is common to all living beings without exception,
from the lowest radiate to the highest vertebrate, but that its structure
is at first identical in all, composed of the same primitive elements and
undergoing exactly the same process of growth up to the time when it
assumes the special character peculiar to its kind ;" and the only real
diiference between oviparous and viviparous animals is that in the Ovip-
ara the fecundated egg is discharged from the body of the female and
