nS 



POPULAR SCIENCE MONTHLY. 



Fig. 9 Albrecht Koei.uker. Born 1817. 



vertebrate embryology of high merit. His portrait is shown in 

 Fig. 9. 



Huxley took a great step towards unifying the idea of germ-layers 

 throughout the animal kingdom, when be maintained, in 1849, that the 

 two cell-layers in animals like the hydra, and oceanic hydrazoa, corre- 

 spond to the ectoderm and endoderm of higher animals. 



Kowalevsky, whose portrait is shown in Fig. 10, made interesting 

 discoveries of a general bearing. In 1866 he showed the practical 

 identity, in the early stages of development, between one of the 

 lowest vertebrates (Amphioxus) and a tunicate. The latter had 

 up to that time been considered an invertebrate, and the effect of 



