STUDIES IN THR RETINA. 349 



It may be noted in passing that tlie expulsion of the nncleo- 

 phism, and the consequent contraction or balling together of 

 nuclei into compact masses of refractive chromatin, is not a 

 new phenomenon/ but in this present case the contractions 

 are spontaneous, and fulfil a distinct purpose. 



It is worth while pointing out that there is ground for 

 believing that the fluid is discharged from the nuclei with 

 some force. It is only on such a supposition that Ave can 

 explain many of the phenomena of rod-formation, such, for 

 nstance, as the forcing of the long cone through the whole 

 layer of rods in its earliest stages (see Part I, figs. 2 a, d), 

 the changes of shape, and the shifting of the contents of the 

 young rods in certain stages, in consequence of another rod- 

 vesicle being thrust in among them (see Part I, figs. 4 and 7, 

 c^ and rj). Lastly, in retinas which are either embryonic or 

 have not yet become functional, no rods being yet formed, 

 the pigmented layer is in close contact with the external 

 membrane of the retina. It is apparently only pushed away 

 by the protrusion of the rod-vesicles. This, again, implies 

 some force, especially when we remember the tendency of the 

 pigmented cells to push towards the light. 



An objection, however, may be raised against this sugges- 

 tion of pulsations, or at least against the suggestion that 

 these pulsations pass through the retina in waves, as an 

 explanation of the zonal arrangement of the two nuclear 

 phases. 



It may be asked why, if this zonal arrangement represents 

 a series of pulse waves, the zones do not alter their relative 

 positions in different retinas ? Why is it that, in all eyes, the 

 vesicular are always on the inner side, and the contracted on 

 the outer side of the inner and middle nuclear layers ? If 

 there were waves, some preparation ought to show these 

 waves in other positions. The explanation of this I take to 

 be as follows : — The source of the fluid is probably the blood- 

 vessels on the inner or proximal side of the retina. Hence the 



' Dr. de Nabias has seen it in I'ulmonate Gastropods; see 'Trav. Station 

 Zool. Arcaclion,' Annee 1S99, pp. 36 — 38. 



