490 J. T. GEADON. 



We have seen that, in the development of the optic nerve 

 of the frog there is a period of slow growth, followed by one 

 of great activity, and we have felt justified in ascribing this 

 sudden outburst of activity to a greatly increased flow of 

 lymph into it by means of the elaborate system of minute 

 channels that follow the course of each fibril of the epiblastic 

 trabeculee, and consequent upon the formation of the arach- 

 noid sheath and the enclosure of the subarachnoidal lymph 

 space. 



We have therefore shown that the cells of the optic stalk 

 perform the following three functions : 



1st. They conduct the nerve-fibres, which, in their turn, 

 resolve the constitution of the cells of the stalk, so that they — 



2ud. Provide the nerve-fibres with a supporting framework 

 which — 



3rd. Provides the whole interior of the optic nerve with an 

 elaborate system of minute lymph channels. 



Alphabetical List of Literature referred to. 



1. AssuETON, K. — " Ou the Development of the Optic Nerve of Vertebrates, 



and the Choroidal Fissure of Embryonic Life," ' Quart. Jouru. Micr. 

 Sci.,' vol. 3i, 1892. 



2. Cajal, Ramon y. — " Sur la fine structure du lobe optique dcs oiseaux, ct 



sur I'origine reele des nerfs optiques," ' Monthly luternatioual Journal 

 of Anatomy and Physiology,' vol. viii, parts 9 and 10, 1S91. 



3. rKOiULr, A. — "Ueber die Entwickelung des Sehnerven," 'Anat. Anz.,' 



vi Jahrg., 1891. 



3a. " Entwickelung des Auges," * Ilaudbuch der vergleichenden und 



experimcutellen Entwickelungshlehre der Wirbeltiere," 0. Hertwig, 

 Bd. ii, Abt. 2, Jena, 1905. 



4. Keibel. — "Ueber die Entwickelung des Sehnerven," ' Deutsch. Mcdizin 



Wochenschr.,' xv Jahrg., 1889. 



5. KoLLlKEB. — " Zur Entwickelung dcs Auges und Geruchsorgaus mcnsch- 



lichcr Embryonen," ' Eestchrift der Universitiit Zurich dargebracht,' 

 Wiirzburg, 1883. 



