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POPULAR SCIENCE MONTHLY. 



Recent Tendencies. Experimental Embryology. — Soon after the 

 publication of Balfour's great work on ' Comparative Embryology/ a 

 new tendency in research began to appear which led onward to the estab- 

 lishment of experimental embryology. All previous work in this field 

 had been concerned with the structure or architecture of organisms, but 

 now the physiological side began to receive attention. Whitman has 

 stated with great aptness the interdependence of these two lines of 

 work as follows : " Morphology raises the question, How came the 



Fig. 12. Oskar Hertwig in 1890. 



organic mechanism into existence? Has it had a history, reaching 

 its present stage of perfection through a long series of gradations, the 

 first term of which was a relatively simple stage? The embryological 

 history is traced out, and the paleontological records are searched, until 

 the evidence from both sources establishes the fact that the organ or 

 organism under study is but the summation of modifications and 

 elaborations of a relatively simple primordial. This point settled, 

 physiology is called upon to complete the story. Have the functions 

 remained the same through the series ? or have they undergone a series 

 of modifications, differentations and improvements more or less parallel 

 with the morphological series?" 



