86 RICHAED ASSHETON. 



medicinische Wochenschrift/ 7th February, 1889, p. 115, 

 which is as follows : — "Ueber die Entwickelung des Sehnerven. 

 — Bei alien Amnioten bilden sich die Nervenfasern in dem un- 

 teren, mit der Netzhaut-anlage in verbindung stehenden Theil 

 des Augenblasenstieles ; eine secundare Losung der oberen 

 Wand vom Pigment Blatt der Retina und eine Verschmelzung 

 derselben mit der eigentlichen Eetina-anlage findet nicht statt. 

 Praparate von Reptilienembryonen (Lac : mural und Tropidon 

 natrix), welche mit Boraxcarmin gefarbt und mit Picrinsaure 

 nachbehandelt sind, zeigen ferner, dass, bei diesen Thiere 

 wenigstens, die erste Sehnervenfasern von der Peripherie cen- 

 tralwarts wachsen. Es ist demnach hochstens wahrschein- 

 lich, dass sie aus der Ketina-anlage hervorwachsen, wenn 

 ihr Ursprung dort auch nicht direkt nachgewiesen werden 

 konnte." 



The suggestion that the fibres of the optic nerve either 

 develop from cells within the retina and grow towards the 

 brain, or that they develop in the brain, and grow towards the 

 retina, and are not [formed by the transformation of the cells 

 of the optic stalk, was first discussed as a matter of theory by 

 His in the year 1868. 



His (10) at that time maintained, as he has so ably demon- 

 strated in a more recent work (11), that nerve-fibres are out- 

 growths from nerve-cells ; and holding that there are no 

 nerve-cells along the optic stalk, he suggested that the fibres 

 of the optic nerve must grow from cells probably in the brain 

 along the optic stalk to the retina. 



With him in the main agreed W. Miiller (20), Mihalkovics, 

 and Kolliker, though they difi'ered as to the direction of the 

 growth of the fibres. 



Certain other embryologists, however, were not convinced 

 by what was little more than suggestion ; among them was 

 Balfour (1, p. 493), who wrote, " There does not seem to me 

 to be any ground for doubting (as has been done by His and 

 Kolliker) that the fibres of the optic nerve are derived from a 

 dififerentiation of the epithelial cells of which the nerve is at 

 first formed;" and Balfour's opinion seems to have been held 



