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Their geological history has been very thoroughly studied; not only are we familiar with all their adult characters, but even their embryology is well known to naturalists. It is, indeed, wonderful that the mode of growth of animals which died out in the Carboniferous period should be better known to us than that of many living types.
While Cuvier and his followers traced these four distinct plans, as shown in the adult animal, Baer opened to us a new field of investigation in the embryology of the four types, showing that for each there was a special mode of growth in the egg.
M. Kovalevsky writes to me from Naples, that he has now carried these observations yet further, and should his results be well established, the whole will form a discovery of the very greatest value. Thus, if we may rely on embryology, ever the safest guide in classification, it seems that we have at last gained a clue to the source whence the Vertebrata were derived.
It is just as much more difficult and complex as man's organisation is more elaborate than the structure of the rocks. When we approach this task, we find an auxiliary of the utmost importance in the comparative anatomy and embryology of two lower animal-forms. Both of these animals are very instructive.
"Embryology is an ancient manuscript with many of the sheets lost, others displaced, and with spurious passages interpolated by a later hand." It is hard to construct a syllogism, showing the force of the argument from Embryology. Try it.
An understanding of the characteristics of embryological thought at the beginning of the seventeenth century may enhance appreciation of later developments. During the latter part of the sixteenth century, the study of embryology was, for obvious reasons, most often considered within the province of anatomy and obstetrics.
The correlative action of these laws under the universal influence of the struggle for existence, or as we may say in a word, with Darwin "natural selection," is entirely adequate to explain the whole process of embryology in the light of phylogeny.
William H. Howell, Johns Hopkins, '81. He was succeeded in 1892 by Dr. Warren P. Lombard, Harvard, '78, who held both Professorships until 1898, when Dr. Huber, at that time Assistant Professor of Anatomy, was made Director of the Histological Laboratory, becoming Junior Professor in 1899 and Professor of Histology and Embryology four years later.
The science of embryology shows that this rule holds good without exception throughout the whole range of the animal world, including man; and botany shows the same principle at work throughout the vegetable world.
It is true, of course, that this evidence is peculiarly significant, because in some ways it is more direct than that of the other categories already outlined. But it must not be forgotten that the doctrine is already securely founded upon the basic principles of anatomy and embryology. Science must treat the data of this category by different methods and must view them in different ways.
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