56 H. M. BERNARD. 



that they are merely nuclei of the middle layer passing out- 

 wards to become rod nuclei, and apparently flattened agaiust 

 the same taugentially arranged cytoplasmic tissue as that 

 wliicli detains the refractive matter in the manner described 

 above. But the difficulty is not quite so simple as tliis, viz. 

 that the stoppage of the nuclei going outwards is due to tlie 

 presence of taugentially arranged tissue, or even to a mutual 

 blocking of the way on the part of the nuclei moving outwards 

 and of pigmented matter moving inwards. That tliis latter 

 is not the cause is clear, because we find the same stoppage 

 of the refractive matter even when, as in old eyes, nearly all 

 the middle nuclei have passed outwards (see fig. 21). I'liat 

 other subtler complications are present can be gathered from 

 the fact that the '' rod fibres " often expand so as to form 

 chambers in the outer reticular layer, and clumps of matter, 

 often taking nuclear stains, may be seen in various conditions 

 within these chambers. The relations of these clumps of 

 staining matter to the terminal expansions of the " rod fibres" 

 is not easy to ascertain ; it is clearly necessary to keep them 

 distinct in our minds. Borysiekiewitz, who, I believe, is 

 the first to figure these chambers/ took them for a new and 

 hitherto undiscovered layer of cells, the " nuclei of which may 

 sometimes be seen dividing." This description, however, does 

 not apply to any eye I have yet examined, for I have found 

 them in all stages of formation, sometimes in patches, some- 

 times all along the retina (cf. figs. 20, 22, and 24). A com- 

 parative study has convinced me that they are, as stated, 

 merely expansions of the inner ends of the '' rod fibres " 

 round some peculiar mass of staining matter. Similar masses 

 occur in the cytoplasmic chambers between the rod nuclei 

 and the outer reticular layer in the frog, as shown in fig. 25, 

 h and d. I can regard them, therefore, only as form-phases 

 expressive of some physiological activity, the significance of 

 which, so far as 1 have been able to unravel it, will bo 

 explained in a later paper. 



But whatever is the real structure of the outer reticular 

 ' Figured in lbS7, but ouly claimed ab a new " ceil " layer iu ISOi. 



