56 



Goronowitsch calls attention to the fact that a proliferation of 

 ectoderm for the formation of mesoderm such as he describes in the 

 bird, is not found in Amphioxus, and concludes that it must have 

 been phylogenetically introduced with the Selachii. I would add to 

 this statement that the origin of true cartilage bears the same date. 



The chief points in which the ontogenetic differentiations of the 

 ectoderm in Necturus differ from the description given by Goro- 

 nowitsch for the bird, may be summarized as follows: 



1) The neural crest arises in two, not three, divisions. 



2) Each division contributes directly to the formation of the 

 peripheral nervous system. 



3) They do not constitute merely a nerve supporting tissue, but 

 give rise to ganglion cells which "spin" motor as well as sensory 

 fibres. 



4) Cells arising from the ectoderm and endoderm respectively are 

 differentiated from one another until a late stage of embryonic deve- 

 lopment by the yolk globules they contain. 



5) A homogeneous tissue composed of cells wandering from the 

 neural crest, ectoderm, and axial mesoderm does not exist. 



6) There is consequently no homologue of the "periaxial Strang". 



7) Wandering cells from neural crest and ectoderm give rise to 

 the cartilages of the head. They may contribute to the formation of 

 other tissues, but I find no evidence that they take part in the for- 

 mation of the "cutis" as Goronowitsch suggests. 



Aug. 25./93, Marine Biological Laboratory, Woods Holl. 



Berichtigung 

 zu dem Aufsatz von R. Penzo, Jahrgang VIII, No. 21 und 22. 



S. 740, Z. 29 von oben ist zu lesen: centrales Ende im Ganglion, peripheres Ende 

 im Facialis. — S. 741, Z. 2 von unten : ganz jener entgegengesetzt. — S. 743, Z. 5 von 

 oben : dafs diese anastomotischen. — Auf S. 743 oben ist ein Satz zwei mal, mit beinahe 

 denselben Worten (durch Klammern eingeschlossen) gedruckt worden. 



Der Herr Verfasser fügt hier noch die Bemerkung bei, dafs, im Auszuge, das Wort 

 Ende nicht im organisch-anatomischen Sinne, sondern in rein mechanischer Bedeutung 

 zu nehmen ist. 



Frommannsche Buchdruckerei (Hermann Pohle) in Jena. 



