646 



Aufsätze. 



The origin of tlie segmental duct in Elasmobranchs. 



By J. Beard, Freiburg i/B. 



Aus dem Auatomischen Institute zu Freiburg i/B. 



It is a remarkable circumstance that Hensen's^) account of the 

 epiblastic origin of the segmental duct in the rabbit should so long 

 have remained unaccepted, or at any rate without actual refutation. 

 The time of publication of his researches, viz. before and about the 

 period of Semper's^) and Balfour's^) brilliant investigations, should 

 certainly have yielded the statement better attention at the hands of 

 morphologists. Balfour and (more recently) Mihalkovics*), it is true, 

 denied such a mode of formation, and Balfour stated that the duct 

 has a mesoblastic origin in Scyllium, one of the genera in which I 

 now record a similar result to Hensen's. 



Balfour actually saw the duct in the epiblast of Scyllium embryos, 

 — this is certain from his descriptions. Semper, who first recognised 

 the significance of the duct, accepted Balfour's view, as he had no 

 stages young enough to examine the matter lor himself. It is 

 incomprehensible that he should have disregarded Hensen's notice, 

 seeing that the discovery was really of very great importance for 

 the views of the origin of Vertebrates which he advocated. 



Spee ^) nearly ten years later confirmed Hensen's account in the 

 Guinea pig , without attaching any greater importance to the fact 

 than finding it satisfactory as establishing the rule of the histologist 



1) Hensen, Virchow's Archiv, Bd. XXXVII, p. 81. 



,, Archiv f. mikrosk. Anat., Bd. II, 1867. 



„ Beobachtungen über die Befruchtung etc. Archiv f. 

 Anat. u. Physiol., 1875, p. 370—371. 



2) Sempek, Urogenitalsystem der Plagiostomen. Arbeiten des Würz- 

 burger Instituts, Bd. II, 1875. 



3) Balfoijb, Elasmobranch Fishes, p. 127 et seq. 



4) MiHALKovics, Entwickl. des Harn- und GescWechtsapparates der 

 Amnioten. Krause's Internat. Monatsschr., 1885. 



5) Spee, Über direkte Beteiligung des Ectoderms etc. Archiv f. Anat. 

 u. Physiol., 1884. 



