STUDIES IN THE RETINA. 453 



dragging the cytoplasmic reticulum after them. Such 

 figures might be multiplied indefinitely, and, moreover, 

 taken from nearly every retina that is closely enough exa- 

 mined. I reserve full discussion of this somewhat revolu- 

 tionary conception of the retina as a syncytium for another 

 communication. But in the meantime I feel compelled to 

 state my conviction that the rods are not the prolon- 

 gations of 'Wisual cells/^ but protrusions of the 

 cytoplasm of the retinal syncytium, each, at least 

 in the Amphibia, dominated by a nucleus. 



Passing on from this digression, and regarding it for the 

 moment as indifferent how we describe the rods in their 

 relations to the nuclei, the evidence is abundant, as I shall 

 now endeavour to show, that these nuclei are the centres of 

 the physiological activity which gives rise to the rods. 



In the first place, a great part, if not all of the fluid or 

 hyaline matter, here always spoken of as fluid, which first 

 causes the vesicle to protrude, comes from the associated 

 nuclei. 



Fig. 17 can hardly admit of any other interpretation than 

 that fluid is extruded by the nuclei into the inner limbs of rods. 

 If it is objected that these figures might as easily be inter- 

 preted as representing phenomena due to the stimulation of 

 fixing agents, this argument will not apply to fig. 23, 

 where we see a " double cone/" in which one nucleus is still 

 large and vesicular, while the other is collapsed, because its 

 fluid contents have been discharged into the base of the cone 

 belonging to it. Indeed, a study of cones with their basal 

 vacuoles makes it very evident that the fluid of these vacuoles 

 has been derived from their nuclei. Large vesicular nuclei 

 in the position of cone-nuclei, i. e. well within the membrana 

 limitans externa, are very common and in striking contrast 

 to the more condensed i"od-nuclei (figs. 16, a, h, and 18). 

 The same contrasts may also be found in the other nuclear 

 layers, but here, again, it is impossible to give in this paper 



' For the correct interpretation of " double cones " in the Amphibia s^e 

 Part I, p. 33. 



