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Nachdruck verboten. 



Ectodermal or Mesodermal Origin of the Bones of Teleosts ? 



By K, G. Harrison, Baltimore, U. S. A. 



[Aus dem Anatomischen Institut zu Bonn,] 



With 3 Figures. 



In a comprehensive paper V) published a short time ago, Dr. H. 

 Klaatsch seeks to demonstrate that the skleroblastic cells of verte- 

 brates are derived exclusively from the ectoderm. In support of this 

 view the author records many observations, covering a wide field. It 

 would be quite out of place here to enter into any discussion of the 

 generalizations made in this work, but in as much as the account 

 given of the development of the horny fibrils and the fin-rays of fishes, 

 is directly opposed to my own published observations ^), I cannot but 

 call attention to certain sources of error, which, in my judgment, 

 have escaped Dr. Klaatsch's notice. 



One of the salient points of Dr. Klaatsch's paper is that the 

 free border of the fin -folds, both median and paired, is one of the 

 principal regions of proliferation, where the skleroblastic cells are 

 generated, and crowding thence into the interior, they give rise to the 

 homy fibrils, fin-rays, and even to the axial skeleton. Dr. Klaatsch 

 arrives at this result chiefly through the study of Elasmobranch fins, 

 although he extends the same view to cover the bony fishes also. 



After carefully re-studying my material I am quite unable to 

 come to this conclusion. The material consisted of serial sections, 

 5 fj- thick, of S. Salar, in all stages from 6 mm to 2,5 cm in length. 



Sections through the median fins show most clearly that the 

 basement membrane underlying the epidermis maintains its integrity 

 throughout, and moreover that the membrane is even still more 

 sharply defined at the free border of the fin-fold. The distinctness 

 of the membrane, however, varies considerably with the technique 

 employed. Specimens killed in a saturated solution of corrosive sub- 

 limate in five percent, acetic acid, and stained in Delafield's haemato- 

 xylin show the membrane as a sharp blue line. It is even clearer 



1) H. Klaatsch, Ueber die Herkunft der Skleroblasten. Morph. 

 Jahrb., Bd. 21, Heft 2. 



2) R. G. Harrison, Ueber die Entwickelung der nicht knorpelig vor- 

 gebildeten Skeletteile in den Flossen der Teleostier. Archiv f. mikrosk. 

 Anat., Bd. 42. 



