THE GROWTH IN LENGTH OF THE 

 VERTEBRATE EMBRYO 



LECTURE I 



The mode of growth of the main axis of the Vertebrate Embryo 

 has been for a good many years a subject of controversy among 

 Comparative Anatomists and Embryologists. The problem is not 

 such an easy one as it seems at first sight to be. 



From a zoological point of view it is a very important question ; 

 because according to the way in which we are disposed to answer 

 it we shall form our ideas as to the relation which the main axis 

 of the vertebrate body bears to the main axis of the bodies of 

 animals of other phyla. Also upon this problem depends to a 

 large extent the view we take about metamerism. An Annelid is 

 a distinctly metamerically segmented animal so is a Vertebrate. 

 Is this similarity a case of homology or of convergence? And 

 what is the relation that the metamerism of the one bears to that 

 of the other? 



The problem of the growth in length of the Vertebrate Embryo 

 may be said to have originated with the essay by Prof. Wilhelm His 

 published in the year 1874 on the formation of the trout embryo 

 ("Ueber die Bildung des Lachs Embryo/' Sitzungsberichte der 

 naturforschenden Gesellschaft zu Leipzig, i. Jahrgang (1874), S. 30); 

 the theory of the mode of growth in length of the embryo 

 enunciated in this paper was expanded in subsequent papers, 

 among which may be mentioned his well-known work Unsere 

 Korperform und das physiologische Problem ihrer Entstehung, 

 published in the same year. 



The theory which His then put forward has been termed the 

 concrescence theory. It is with respect to embryos of Teleosteans 

 and Elasmobranchs that one is most inclined at first sight to 

 adopt this theory of the growth in length of the Vertebrate. 



