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Embryology teaches us that the eggs from which all animal forms evolve are all practically alike so far as one can ascertain by microscopic examination, no matter how diverse may be the forms which will evolve from them, and this resemblance is maintained even when the embryo of the higher forms begins to manifest traces of its future form.
In order to appreciate fully this remarkable fact, and especially to secure the sound basis we seek for the genealogical tree of the vertebrates, it is necessary to study thoroughly the embryology of both these animals, and compare the individual development of the Amphioxus step by step with that of the Ascidia. We begin with the ontogeny of the Amphioxus.
In 1651, about two months before publication of Highmore's History of Generation, a work appeared which marks another period in seventeenth-century English embryology. William Harvey, De Motu Cordis almost a quarter of a century behind him, now published De Generatione Animalium, the work he said was calculated "to throw still greater light upon natural philosophy."
For the last hundred years, however, the importance of a study has been recognised which does actually reveal to us in no small degree the processes by which the human foot is manufactured, so that in our endeavour to lay our hands upon the points of difference between the kind of design with which the foot itself is designed, and the design of the model, we turn naturally to the guidance of those who have made this study their specialty; and a very wide difference does this study, embryology, at once reveal to us.
Only in the latter cases the combinations of the different forces that appear as "movement" in the phenomenon are much more intricate and difficult to analyse than in the former. Our study has led us to the conclusion that in the whole evolution of man, in his embryology and in his phylogeny, there are no living forces at work other than those of the rest of organic and inorganic nature.
With all its mastery of the laws of heredity, of cytology, and of embryology, it cannot tell why a man is a man, and a dog is a dog. No cell-analysis will give the secret; no chemical conjuring with the elements will reveal why in the one case they build up a head of cabbage, and in the other a head of Plato.
Spencer's classifications. Nor do the minor deviations from this general parallelism, which look like difficulties, fail on closer observation to furnish additional evidence; since those traits of a common ancestry which embryology reveals are, if modifications have resulted from changed conditions, liable to be disguised in different ways and degrees, in different lines of descendants. Mr.
The principles of classification exemplified, the methods of description illustrated, the rules of nomenclature tested, what matter is it whether the gran maestro has chosen this or that string to play the air upon, when each has compass enough for all its melody? Still more forcibly does this comment apply to the elaborate and ample division of the work embracing the Embryology of the Turtle.
On account of the present limitations of time, the subject of classification will be combined with comparative anatomy; embryology will be taken up together with these subjects; palæontology will be the main subject of the next discussion, which will include also a brief statement of the meaning of distribution. Then we will be prepared to study nature to see how evolution works.
In so far as it deals with structures in the making, embryology is a study of anatomy, but as it is concerned primarily with all of the plastic remodeling which animals undergo during the production of their final forms, it is an independent study.
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