82 Trans. Acad. Sci. of St. Louis. 



definitely distinguishing between homologous and analogous 

 structures. 



After Cuvier's death the center of zoological progress 

 moved to Germany, where to a greater degree than anywhere 

 else the study of the minute structure of animals and their 

 development by the aid of the compound microscope had 

 given the science an immense impetus. 



Contemporaneous with Cuvier was Johannes Miiller ( 1801— 

 1858), the greatest of all investigators of animal structure, 

 whose reputation for rapid, exhaustive and accurate observa- 

 tion has never been surpassed. Possessing a remarkable com- 

 prehensiveness of view and unusual skill in dissection, he 

 achieved brilliant results not only in the field of anatomy, but 

 also in that of embryology and physiology. His memoirs upon 

 the structure of Amphioxus and Bdellostoma, two of the lower 

 vertebrates ; on the anatomy and classification of Fishes ; and 

 on the development of Echinoderms, are some of his most im- 

 portant researches, and still stand among the marvels of 

 zoological investigation. 



It is impossible to even enumerate the host of workers 

 of this period who advanced the science in rapid strides, 

 adding far-reaching discoveries in anatomy and embryology 

 and correction of former errors. Reference has already 

 been made to the able embryologist Karl Von Baer, 

 the discoverer of the mammalian egg, who may be said 

 to have really founded the study of embryology. 

 Thompson in England removed the Cirripedia from the 

 group of Mollusca where Cuvier had retained them, and from 

 a study of their development placed them, where they prop- 

 erly belong, with the Crustacea. Siebold established the 

 group Protozoa in its modern signification, separating it from 

 Cuvier's Radiata ; and a decade later (1848), Leuckart finally 

 did away with the Radiata altogether by dividing the remain- 

 der into two groups; namely, the Coelenterata (polyps, me- 

 dusae, etc.), and the Echinodermata (star-fishes, sea-urchins 

 and related forms); two distinct branches which only very 

 superficially resemble each other. Siebold further abol- 

 ished Cuvier's Articulata, transferring the Annelida to the 

 Vermes or worm-group, and proposing the term Arthropoda 



