MODERN BIOLOGY 367 



In regard to his theoretical conception of these conditions, Rathke accepts 

 without reservation Meckel's theory of the lower animal forms that the 

 higher animals pass through during their embryonic life. A more independent 

 theory is developed by him in a treatise tjber die rucks chre it ende Metamorphose 

 der Tiere, in which he records the results arrived at during his research work 

 in comparative embryology. Although full of difficult abstract ideas, this 

 article presents a view — original for the time at which it was written — ■ 

 of a hitherto neglected phenomenon in animal life. The phrase "ruckschrei- 

 tende Metamorphose" is characteristic of the age. Rathke makes a cautious 

 reservation against the confusion of his ideas of metamorphosis with those 

 of Goethe; in the form in which it is presented here, it has in view the regres- 

 sive development which certain organs undergo during their embryonic and 

 early life and which concludes with their total disappearance or survival as 

 rudiments. Rathke cited examples of phenomena of this kind from the entire 

 animal kingdom, but he supports his argument mainly on examples taken 

 from the vertebrates, as for instance the gills and tail of the tadpole, the 

 Wolffian organs, etc. He declares that such organs are either dissolved or are 

 reabsorbed by the rest of the body, or else are knocked off and disappear; the 

 latter occurs if they are horny and lack blood-vessels, the former if they 

 possess blood-vessels by which their substance can be absorbed and made use 

 of in the body. And it always happens, he declares, that such a disappearance 

 of one organ is succeeded by the development of another which takes its 

 place, as for instance the lungs of the frog, which develop according as the 

 gills disappear, or the kidneys in the bird and mammal embryo, which take 

 the place of the Wolffian bodies. Only an entirely altered mode of living 

 during more advanced stages of development can bring about the total loss 

 of previously existing organs, as happens in the parasitic crustaceans. It 

 will at once be realized that here Rathke has shed light on one of the most 

 important problems of modern biology. 



Rathke' s marine-zoological studies 

 But Rathke's activities were not merely confined to embryology; he is also 

 one of those who have opened up for biological research the vast field that 

 the seas have to offer. Cuvier was the first in modern times to draw the atten- 

 tion of science in this direction. Rathke, who was born and grew up in a 

 seaport and who in the course of his travels — in Scandinavia amongst other 

 countries — had his own interest in this field of research stimulated hereby, 

 contributed largely towards awakening it in his countrymen. In this respect 

 he gained much from the acquaintance he made in Bergen with the then 

 priest Michael Sars (1805-69), another of the pioneers of marine research, 

 who presented him with many valuable animal-forms and gave him much 

 information. Of Rathke's work in this sphere may be mentioned his careful 

 description of the lancet-fish — that extremely primitive vertebrate animal 



