344 THE HISTORY AND SCOPE OF ZOOLOGY IX 



activity in the study of Embryology which followed on 

 the publication of the Origin of Species. 



The pre-Darwinian systematists since the time of 

 Von Baer had attached very great importance to 

 embryological facts, holding that the stages in an 

 animal's development were often more significant of 

 its true affinities than its adult structure. Von Baer 

 had gained unanimous support for his dictum, "Die 

 Entwickelungsgeschichte ist der wahre Lichttrager fur 

 Untersuchungen iiber organische Korper." Thus J. 

 Miiller's studies on the larval forms of Echinoderms 

 and the discoveries of Vaughan Thompson were appre- 

 ciated. But it was only after Darwin that the cell- 

 theory of Schwann was extended to the Embryology 

 of the animal kingdom generally, and that the know- 

 ledge of the development of an animal became a 

 knowledge of the way in which the millions of cells of 

 which its body is composed take their origin by fission 

 from a smaller number of cells, and these ultimately 

 from the single egg-cell. Kolliker (Development of 

 Cephalopods, 1844), Kemak (Development of the Frog, 

 1850), and others had laid the foundations of this 

 knowledge in isolated examples ; but it was Kowalew- 

 sky, by his accounts of the development of Ascidians 

 and of Ampliioxus (1866), who really made zoologists 

 see that a strict and complete cellular embryology of 

 animals was as necessary and feasible a factor in the 

 comprehension of their relationships as at the begin- 

 ning of the century the coarse anatomy had been 

 shown to be by Cuvier. Kowalewsky's work ap- 

 peared between the dates of the Generelle Morpho- 



