RATHKE 137 



appeared in I829, 1 Rathke found in an Invertebrate confirma- 

 tion of the germ-layer theory propounded by Pander and 

 von Baer. He was greatly struck by the inverted position of 

 the embryo with respect to the yolk. In following out the 

 development of the appendages he noticed how much alike 

 were jaws and legs in their earliest stage, and how this 

 supported Savigny's contention that the limbs of Arthropods 

 belonged to one single type of structure. In his paper (1832) 

 on the development of the fresh-water Isopod, Ascllus? 

 Rathke returns to this point. Commenting on the original 

 similarity in development of antennae, jaws and legs, he 

 writes, " Whatever the doubts one may have reserved as to 

 the intimate relation existing between the jaws and feet of 

 articulate animals after the researches of Savigny on this 

 subject and mine on developing crayfish, they must all fall to 

 the ground when one examines with care the development 

 of the fresh-water Asellus " (p. 147 of French translation). 



Further comparative work by Rathke is found in the 

 two volumes of Abhandlungen and in a book, Zur Hlor- 

 phologie, Reiscbemerkungen aus Taurien (1837), which con- 

 tains embryological studies of many different types, including 

 a study of the uniform plan of arthropod limbs. Later on 

 Rathke devoted himself more to vertebrate embryology, 

 producing among other works his classical papers on 

 the development of the adder (1839), of the tortoise (1848), 

 and of the crocodile (1866). He laid the foundations 

 of all subsequent knowledge of the development of the 

 blood-vascular system in a series of papers of various dates 

 from 1838 to 1856. The diagrams in his paper on the 

 aortic arches of reptiles (1856) were for long copied in every 

 text-book. 



Rathke was a foremost worker in another important line 

 of embryological work, the study of the development of the 

 skeleton and particularly of the skull. We shall discuss the 



1 Untersuchungen iiber die Bildiing und Entwickclung der Fluss- 

 Krebses, Leipzig, folio, 1829. Preliminary notice in his, pp. 1093-1100, 

 1825. 



" " Untersuchungen iiber die Bildung und Entwickelung der Wasser- 

 Assel.," Abh. s-. Bild. u. Entwick.-Gesch., i., pp. 1-20, 1832. Translated in 

 Ann. Sci. nat. (2), ii., (ZooL), pp. 139-57, 1834. 



