THE CRANIAL GANGLIA IN AMEIURUS 



31: 



A comparison of Koltzoff's excellent paper ('02) on the embry- 

 ology of Petromyzon with the work of Johnston ('05 b) on the nerve 

 components of the same type will serve to introduce the point of 

 view from which the author has worked the early stages of the 

 ganglia in Ameiurus. KoltzofT does not list a single nerve compo- 

 nent paper in his bibliography and was in fact working primarily on 

 the segmentation of the head, and only incidentally on the origin 

 of the ganglia. The results of these two papers are summarized in 

 the following diagram : 



TABLE I 



Summarizing the results of Koltzoff's work on the development of the ganglia in 

 Petromyzon, and of Johnston's on the adult structure of the same form 



PROF. OR TRIG. OR 



TRIG. I. V TRIG. II. V 



Neu. Crest.. Neu. crest Neu. crest Neu. crest Neu. crest Neu. crest Neu. crest 



Segmental 



sc .K 



o <-> 

 o ~~^ 



I { D. L. Plac. . D.L. Plac. D.L. Plac. D.L. Plac. D.L. Plac. D.L. Plac. D.L.Plac. 



Ep. Plac Ep. Plac. 



Ep. Plac.Ep. Plac. 

 Segmental 



§ a 

 S S 



co o 



General Prof. N. 



Cutaneous . and Gan.. 



Trig. N.Gen. Cut. 



Gen. Cut. 

 Gen. Cut. X. 



and Gan.. VII IX. 



Segmental 



Lat. X. 



Acustico- Lateralis Lateralis Lateralis Lateralis Not 



Lateralis . . . Prof Trig VII Auditory. IX Segmental 



Communis 

 [ or Visceral Com. VII. 



Com. X. 

 Com. IX. Segmental 



It will be seen at a glance that every nerve into whose ganglion 

 cells derived from the epibranchial placode enter contains in the 

 adult visceral fibres; every nerve to whose ganglion the dorso- 



