A CENTUEY OF ZOOLOGY IN AMEEICA 427 



value of critical statistical analysis in the interpretation 

 of biological data. A thorough training in mathematics 

 is now found to be hardly less important for the biologist 

 than is a knowledge of physics and chemistry, for the 

 science of biometry has become one of the most important 

 adjuncts to the study of genetics. 



Comparative Anatomy and Embryology. 



Comparative Anatomy. Upon the foundations laid 

 down by Cuvier a century ago the present elaborate 

 structure of comparative anatomy of animals, both verte- 

 brate and invertebrate, has been developed. Vast as is 

 the present accumulation of facts and theories many 

 important problems still await their solution. Jeffries 

 Wyman was long a leader in this field, where many 

 workers are now engaged. 



Embryology. The embryological studies, so bril- 

 liantly begun by Von Baer early in the nineteenth cen- 

 tury, are still in progress. They have now been extended 

 to the groups more difficult of investigation and into the 

 earliest stages of fertilization and implantation in the 

 mammals. Artificial cultural methods have yielded 

 important results. Louis and Alexander Agassiz, Mark, 

 Minot, Brooks, Whitman, Conklin and E. B. Wilson have 

 taken prominent parts in this work. 



In the early nineties embryological studies were 

 directed to the arrangement of cells in the dividing egg, 

 and there was much discussion of ''cell lineage" in 

 development. Valuable as were these studies they threw 

 comparatively little light on the general problems of 

 evolution. 



Experimental Embryology. A more fertile field, 

 developed at the same period and a little later, was found 

 in experimental embryology. The discoveries made by 

 Driesch and others in shaking apart the cells of the divid- 

 ing egg or by destroying one or more of these cells gave 

 a new insight into the potency of cells for compensatory 

 and regenerative processes. These studies attracted 

 many able investigators, who made still further advance 

 by subjecting the germ cells, developing eggs, embryos, 



