STUDIES IN THE RETINA. 449 



not free, like Max Schultze's needle-like prolongations of his 

 " Faserkorb/' but rather as thickenings of the stretched 

 membrane. On these threads clumps of staining matter soon 

 appear (fig, 13, c). In the diagram, fig. 11, the system is 

 drawn very symmetrically from the nucleus outward, but this 

 is not by any means usually the case. The nearest approach 

 to it has been found in the axolotl, preparations of which 

 inspired this diagram. Fig. 29, b, represents moi'e truly the 

 ordinary conditions. We have a gradual formation of the 

 symmetrical system of strise towards the distal ends of the 

 inner limbs (though usually quite irregularly), and when 

 formed it passes on to the outer limbs. Thei-e is some evi- 

 dence that this is also what takes place in the human rods 

 and cones, for the "fibrillation" is said to be limited to the 

 outer portions of the inner limbs (cf . ' Quain's Anatomy,' 

 1894, vol. iii, part 3, p. 49, fig. 52, after Schwalbe). 



Some variation seems to occur in the numbers of the longi- 

 tudinal threads on the outer limbs ; they are sometimes very 

 numerous (e. g. newt, fig. 30), at others veiy spai-se ; and this 

 is not only the case in different Amphibia, but in different 

 specimens of the same. Figs. 3 and 6 are from different 

 frogs; in one case the threads are crowded, and in the other 

 quite far apart : the rods in this latter case have been greatly 

 stretched, but one does not see why that should lessen the 

 number of striae. The significance of some of the irregularities 

 of this system of striae ^ will be better understood when we 

 have described the connection between these threads and the 

 contents of the vesicles in whose walls they occur. 



The rods, then, are delicate protoplasmic vesicles, in the 

 thin walls of which staining threads occur. In the walls of 

 the outer limbs these threads are usually more or less 

 beaded with clumps of staining matter. The claim made by 

 Max Schultze and Hoffmann (see the figures and plates re- 



' The spiral twist of tlie stiise on tlie outer limbs has been rightly attributed 

 to torsion. I have only seen it, and then very marked, on rods broken off 

 like that shown in fig. 13, c. 



