134 THi; K.MIMYOIXXJICAL CRITERION 



the alimentary canal ; he observed and interpreted rightly 

 the formation of the medullary folds. The circular blasto- 

 pore in the frog in later years often went by the name of the 

 anus of Rusconi. 



In France Dutrochet l investigated the ftetal membranes 

 in various vertebrate classes ; Prevost and Dumas studied 

 the very earliest stages of development in birds, mammals 

 and amphibia (Ann. Sci. uat., ii., iii., 1824, xii., 1827). 



A little later came Duges' studies of the osteology and 

 myology of developing amphibia (1834),- and Coste's careful 



researches into the early develop- 

 mental history of mammals. 3 



It was in 1825 that Heinrich 

 Rathke (1793-1860), published his 

 famous discovery of gill-slits in the 

 embryo of a mammal, 4 a discovery 

 which aroused considerable interest, 

 and greatly stimulated embryological 

 research. He describes how in a 

 young embryo of a pig he saw four 



- Gi ":f s U ; e . * slits in the region of the neck, going 

 Embryo. (After Rathke.) 



right through into the oesophagus. 



They were separated by partitions which he called Kictnen- 

 bogen (gill-arches), and immediately in front of the first gill- 

 slit lay the developing lower jaw. He compared these gill- 

 slits with those of a dogfish. We reproduce his drawing of 

 the pig-embryo (Jsis, PI. IV., fig. i). 



Later in the same year Rathke discovered gill-slits in the 

 chick/" in this case finding only three. He described growing 

 out from in front of the first slit a structure which he 

 compared to the operculum or gill-cover of a fish. 



These discoveries were confirmed and extended for the 



1 See review by Cuvier, Mem. Afus. Hist. H<I/., iii., pp. 82-97, 

 1817. 



- Mem. SaiHins ctr<in^crs, vi. Kxtract in Ann. Sci. rial. (2) i. (Zool.), 

 pp. 366-72, 1834. 



:t Recherches sur la generation ties Manuni feres, 1834. Embryogcnie 

 comparee, 1837. 



1 " Kiemen bey Saugthieren," Isis, pp. 747-9, 1825. 



' " Kieineii bey Voyeln," /sis, pp. 1100-1, 1825. 



