STUDIES IN THE EETTNA. 815 



filaments are continuations of the tlireads of the intra-nuclear 

 I'eticulum. 



These facts and illustrations — and the latter could be 

 multiplied indefinitely — show that the nuclei of the middle 

 layer are connected together not only inter se^ but that 

 filaments run from the nuclei that border the layer into the 

 two reticular layers, proximally towards the ganglionic nuclei 

 (figs. 15, 17 c, and 18 d) and distally towards the rod-nuclei 

 (figs. 18 a, h, d, and 19). 



Evidence for the Existence of luternuclear Fila- 

 ments between the Nuclei of the Outer Nuclear 

 Layer (the Rod-nuclei). 



In the Amphibia this layer is thin, for the rods are stout, 

 i.e. very nearly as thick as the nuclei. These nuclei, in 

 crowding outwards, are often tightly packed, and hardly form 

 a double layer. Junctions between them inter se are fre- 

 quently obscured by the coarse masses of intra-nuclear 

 chromatin which characterise the rod -nuclei of all retinas 

 (see below, p. 338) ; figs. 18 b and d shoAv, however, that they 

 do exist. The connecting filaments are sometimes seen 

 bridging intervals ; at others the disposition of the clu'omatin 

 within the nuclei shows that their networks are joined 

 together. Further, the same figures show the nuclei of this 

 layer connected Avith the nuclei of the middle layer, through 

 the outer reticular layer. In figs. 18 & and 19 we have 

 nuclei within or passing through the outer reticular layer 

 on their passage outwards to become rod-nuclei, and these 

 give off filaments towards the nuclei of both middle and outer 

 layers. In fig. 19 the connecting filaments could not be 

 traced through the cytoplasmic strands of the outer reticular 

 layer; they were lost to view, just as they usually are within 

 the cytoplasmic masses which, in the Mammalia, envelop so 

 many of the ganglionic uuclei. But, iu figs. 18 a, h, d, the 

 filaments, being coated with staining matter, can be easily 

 traced through this same Inyer. The dark stellate body in the 



