THE EMBRYOLOGICAL ARCHETYPE 139 



Entwickelungsgeschichte dcs Kopfes der nackten Amphibien) 

 discussed the two different methods of arriving at the 

 "Type" the anatomical method of comparing adults, and 

 the embryological method of comparing embryogenies. 

 Of the embryological method, he says, " Its aim is to dis- 

 tinguish during the formation of the organism the originally 

 given, the essence of the type, and to classify and interpret 

 what is added or altered in the further course of development. 

 Embryologists watch the gradual building up of the organism 

 from its foundations, and distinguish the fundament, the 

 primordial form, the type, from the individual developments ; 

 they reach thus, following Nature in a certain measure, 

 the essential structure of the organism, and demonstrate the 

 laws that manifest themselves during embryogeny " (p. vi.). 

 The embryologists, influenced in this greatly by von Baer, 

 gradually felt their way to substituting for the "Archetype" 

 of pure morphology what one may perhaps best call the 

 embryological archetype. How the transition was made we 

 can best see by following out the course of discovery in one 

 particular line. We choose for this purpose the development 

 of the skull, a subject which excited much interest at this 

 time and upon which much quite fundamental work was 

 done, particularly by Rathke and Reichert 



Following up his discovery of gill-slits and arches in the 

 embryos of birds and mammals, Rathke in two papers of 

 1832 x and 1833 ' 2 worked out the detailed homologies of the 

 gill-arches in the higher Vertebrates. He describes how 

 in the embryo of the Blenny there is a short, thick arch 

 between the first gill-slit and the mouth. A furrow appears 

 down the middle of the arch dividing it incompletely into 

 two. In the anterior halves a cartilaginous rod is developed 

 which is connected with the skull ; these rods become on 

 either side the lower jaw and "quadrate." In the posterior 

 halves two similar rods are formed which develop into 

 the hyoid. The hyoid is at first connected with the skull, 



1 Anat.-phil. Unters. si. d. Kicmenappamt n. d. Zttngenbein, Riga and 

 Dorpat, 1832. 



14 " Bildungs- and Entwickelungs-geschichte des Blennius viviparus," 

 Abhandl' z. Bild. n. Entivick.-Gesch. dcs Mcnschen u. der Thiere, ii., 

 pp. 1-68, Leipzig, 1833. 



