44 H. M. BERNARD. 



astonished me that it has not been noticed before. The only 

 observer who, so far as I can make out, has called attention 

 to the phenomenon is Borysiekiewitz (1. c), who notes, evi- 

 dently with astonishment, two evidences of transmigration 

 {" Ortswechsel'^) of nuclei which he has seen in the human 

 retina. He notes that nuclei may wander outward (1) from the 

 outer nuclear layer into the basal limbs of the cones, and (2) 

 from the middle nuclear layer into the outer nuclear layer 

 through the outer reticular layer. In this latter case it was 

 the characters of the migrated nuclei, exactly like those of 

 the layer they had left, and not at all like those into which 

 they had moved, which convinced him that migration must 

 have taken place. Leaving the subject for the present, it is 

 obvious that such migration of nuclei outwards from the 

 middle nuclear layer would account — (1) for the enormous 

 increase of nuclei needed for the formation of new rods in 

 the growing retina; (2) for the evident movement of cone 

 nuclei outwards to become rod nuclei. 



All students of the retina will expect here some reference 

 to Landolt's "Kolben;'' and rightly, for it must occur to 

 every one that we have here a possible explanation of these 

 structures. This, indeed, has, I believe, already been sug- 

 gested by Krause ; but I have failed to find again the exact 

 passage in which he speaks of the "Kolben" as most pro- 

 bably supplementary elements. I have not, however, been 

 very fortunate in discovering these bodies, although not for 

 want of looking. The structures which I have seen have not 

 resembled those figured either by Landolt ^ or by Dogiel.^ I 

 therefore prefer to confine myself here to saying that the 

 structures I have seen, if they are what Landolt referred to, 

 fully bear out Krause's suggestion — i. e. that the outermost 

 nuclei of the middle layer, even before they leave that layer 

 to join the definite rod and cone nuclear layer, send radially 



1 'Arch. mik. Auat./ vii, 1871, p. 81. 



^ Ibid., xxiv, 1885, p. 451. See this paper for other iuterpretations of these 

 bodies. The autlior quotes Kuhnt as regarding them as transition forms 

 between rods and cones. 



