328 H. M. BERNARD. 



Observations on some of tlie Relations between tlie 

 Protomitomic System of the Retina and other 

 Constituents of that Organ. 



The Cytoplasm. — There seem to be two distinct kinds 

 of cytoplasm in the retina. There is the syncytial framework, 

 consisting of hyaline strands and membranes, and there is the 

 granular refractive substance found massed around certain of 

 the nuclei in such varying quantities and indefinable shapes 

 that no morphological value can be attributed to it. These 

 two must be treated separately. 



a. The Syncytial Framework. — The most obvious func- 

 tion of this is to serve as a support to the more delicate nuclear 

 or protomitomic i-eticulum, although it is hardly likely that this 

 is its only function. With regard to its origin, it is possible 

 to regard it as having been built up of the ectoplasmic 

 layers of what were originally a number of apparently 

 discrete columnar " cells," out of which the retina has been 

 developed; such cells still persist beyond the rim of the retina 

 in what is known as the "pars ciliaris retiuEe." These 

 " cells," lengthening and crowding together in layers, become 

 spindle-shaped. The processes of change may still be seen 

 in the rims of young amphibian retinas (see Part III, p. 33), 

 and may be understood from the diagram fig-. 24. 



I described in Part III how at least the most cha- 

 racteristic portions of the present syncytial framework of 

 the retina, viz. the zonal arrangement of its two reticular 

 layers, may have arisen from the gradual rearrangement of 

 the cytoplasmic strands of these spindle-shaped " cells." It 

 is obvious that such a migration of the nuclei as was described 

 in Part III would necessarily and effectually obliterate all 

 traces of the separate " cells," and it seems only natural to 

 regard the strands and membranes of the resulting syncytium 

 as directly derived from the more stable outer (ectoplasmic) 

 layers of the original "cells." They are clear and glassy, 

 and show no likeness to the granular cytoplasm already noted 

 as occasionally massed round the nuclei. As some coutirma- 



