CH. xxxvin. VON BAER EMBRYOLOGY. 401 



feathers would not be yet grown. Now the study of the 

 different stages of the develop ment of the chicken in the 

 egg, and of all living beings going through the same stages, is 

 called Embryology ', and has become of immense importance 

 in the history of animals. 



You will remember that Harvey, Malpighi, and many 

 other physiologists, occupied themselves with this study ; 

 but no discoveries of very great importance were made in 

 it before the time of Karl von Baer, a Russian anatomist, 

 who was born in 1792. Von Baer was the pupil of a very 

 famous anatomist, Professor Dollinger, and while he was 

 working under him at Wiirzburg he made for him a 

 number of observations upon the growth of the chicken 

 in the egg, which led him to study the embryology of 

 animals, and to discover the remarkable law of which we 

 must now speak. 



Before Von Baer's time it had always been supposed that 

 the many kinds of animals, so different from each other, 

 must be quite unlike from the very first moment that they 

 began to grow, but Von Baer discovered that this is not so, 

 but that the embryos or beginnings of an ox, a bird, a lizard, 

 or a fish, are so like each other that they can only be dis- 

 tinguished by their size ; and, what is still more remarkable, 

 they remain alike till they have been growing for some time. 

 For example, if you could watch the beginning of these four 

 animals, there would be a certain time during which you 

 could see no difference in their form. Then after a while 

 the fish would start off on a road of its own, but still the 

 other three would go on all alike. Then, when they had 

 grown a little bigger, the lizard would branch off, and only 

 the bird and the ox would continue to have the same 



