CHAPTER XIV. 



EMBRYOLOGY AND THE THEORY OF RECAPITULATION. 



BEFORE bringing into the discussion any evidence derived from the study 

 of comparative embryology, it will be well to enquire briefly into the 

 foundations upon which its arguments are based. Here as elsewhere the 

 methods and opinions of the present time are founded on the knowledge 

 and practice of the past : from time to time, it becomes necessary to re- 

 examine the methods currently applied in any special branch of it, and to 

 ascertain how far they are in accord with the general position of the science 

 as a whole. It will be seen in the matter of embryology that as the point 

 of view of the whole science has altered the methods and opinions of 

 workers in this field have also undergone modification, and we must 

 accordingly be prepared for still further changes so as to keep embryo- 

 logical method in accord with the time. A short historical sketch will 

 illustrate this, and at the same time it may give some better insight into 

 the bases of embryological method as it exists at present. 



Embryology as a branch of the science of Botany can hardly be said 

 to have existed before 1840. It is true that there was already some 

 knowledge of the form and position of the germ in Flowering Plants. 

 So- early as the seventeenth century both Grew and Malpighi dissected and 

 described the embryos of various seeds, while Ray, in his Historia 

 Plantarum, founded the distinction of Dicotyledons and Monocotyledons on 

 characters of the embryo. But up to the early decades of the nineteenth 

 century the study of the early stages of development of the individual 

 was not used as a systematic means of elucidation of the relations of 

 plants. This method was introduced by Schleiden, who saw in the history 

 of development the foundation of all insight into morphology. He founded 

 the study of development of the flower, which has had such far-reaching 

 effects on their comparison and systematic arrangement. He also gave 

 special prominence to the initial embryology of the individual plant, and 

 to comparison of the higher forms with the Cryptogams. Almost simul- 

 taneously the details of cellular construction and of apical segmentation 

 in the lower forms were revealed by Naegeli, and as he extended his 



