SARGENT: THE OPTIC REFLEX APPARATUS OF VERTEBRATES. 135 



This condition, he believes, is due to the fact that the brain tissue, in 

 the course of its development, grows around and encloses the fibre. 

 He failed to find the anterior ending, but believes that the fibre may- 

 have the power of growing forward at its anterior end. Posteriorly he 

 finds the fibre coiled within the ventriculus terrainalis. This he de- 

 scribes as the normal condition, at least in the adult. He apparently 

 believes that the fibre, originally formed in the canal, may by shrinking 

 take this convoluted form in the terminal ventricle. Later in this 

 paper I shall describe a similar coiling of the fibre in the fourth ven- 

 tricle and other parts of its course, and attempt to show it to be an 

 unusual and abnormal condition. Studnicka denies that Eeissners 

 fibre is a nervous structure, (1) because of its relations in the ven- 

 triculus terminalis, and (2) because it differs from an axis-cylinder in 

 being homogeneous. Neither of these distinctions holds, as I hope 

 conclusively to show. He concludes that Eeissner's fibre is formed by 

 the secretion of the walls of the central canal in post-embryonal devel- 

 opment, and that the fibre does not later increase in size. I shall dis- 

 cuss farther on both of these points, showing them to be fallacious. 



In my preliminary paper (Sargent, :00), wliich was prepared for the 

 press in June, 1899, and published in January, 1900, I showed that Eeiss- 

 ner's fibre is a preformed structure occurring in the brain ventricles 

 and central canal of all vertebrates, and intimately connected with the 

 nervous system. Kalberlah (:00, pp. 21-24) has criticised my view as 

 to the nature of Eeissner's fibre, on the basis of observations made by 

 him on Acanthias embryos only. He noticed in the canal "sonder- 

 baren Gebilde im Centralkanal " having " etwa das Bild eines Axencyl- 

 inders, dessen Markscheide durch mangelhafte Fixage oder aus audereu 

 Griiuden gequollen glasig erscheint." " Da fand ich bei einem in toto 

 im Midler geharteten Acanthiasembiyo (siehe dazu Fig, 3), bei dem auch 

 wieder solche Pseudoaxencylinder im Centralkanal lagen, an der Pe- 

 ripherie des Eiickenmarks, und zwar an der ventralen Seite, den Sulcus 

 raed. ausfiillend und breit anfliegend, eine ganze Kollektion soldier 

 Fiidenquei-schuitte von der beschriebenen merkwiirdig glasig homogenen 

 Beschaffenheit." '' Diese Fiiden flir physiologische Sekretstrome zu 

 halten, kann ich mich nicht entschliessen, noch weniger allerdings flir 

 praformierte nervose Gebilde, wenigstens nach dem, was ich gesehen 

 habe, und ich glaube sicher, dass dieselben mit dem von Sargent und 

 den anderen beschrieben identisch sind. Ich lialte die Fjiden fiir'Kunst- 

 produkte, und zwar fiir herausgequollene Myelinmassen." Kalberlah's 

 description and figure convince me that he has not seen Eeissner's 



