258 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



Fibrillae by the vom Rath method. Of the four methods of treatment 

 which I have applied to the study of the fibrillae of the eye of Limax, 

 that of vom Rath seems to me to present the best fixation and most 

 faithful representation of the facts. The results differ from those of the 

 Bethe and Prentiss methods in this, that all of the fibrils of the cell are 

 impregnated. From one point of view, this is a drawback, for it makes 

 a study of the individual fibrils difficult. On the other hand, it is 

 good fortune to have some method by which the entire fibrillar con- 

 tents of the cell may be brought to view. Vom Rath's preparations vary 

 much in value. Sometimes the mantle of the rod appears as a homoge- 

 neous, dark-gray covering; but when the impregnation is favorable cross 

 sections of the rod are almost diagrammatic in their distinctness (Plate 4, 

 Fig. 39). The mantle fibrils look like those in an ordinary preparation, 

 except that they less often cohere. The end-bodies appear deep black, 

 and the fibrils of the core very dark and distinct. The matrix between 

 the fibrils of the core, whatever may be its nature, shows no recognizable 

 structure in these sections. Figure 49 is part of a longitudinal section 

 of a rod treated by this method. The mantle appears as a dark-gray cap 

 over the core. Sometimes even in these preparations the mantle is sep- 

 arated from the core. Judging by the size of the cores, it is probable 

 that in some cases the mantle has swollen. It is possible, however, that 

 the core has plasmolized and so separated from the mantle. Figure 46 

 represents an extreme case. The mantle and core are represented con- 

 ventionally in a gray tone. The most interesting thing about such a 

 vom Rath preparation is the fact, that from the end-bodies many deli- 

 cate fibrillae extend across the space between mantle and core. These 

 fibrils are by no means so numerous as those of the mantle, but they give 

 the impression that they are mantle fibrils which were not broken off 

 by the mechanical separation of the mantle and core. It is possible, 

 of course, that these fibrils represent some of the substance either of 

 the end-bodies or of the core fibrils which has been pulled through the 

 periphery of the core. 



With the exception of the conditions last described, ordinary sections, 

 such as Hesse has used, show all the details of the fibrils in the rod, 

 which this special method reveals. Inasmuch as the other methods 

 which I have used do not contribute anything further to our knowledge 

 of the rod, the foregoing description must suffice for it. 



In vom Rath preparations there is abundant evidence (thanks to the 

 accessory retina) of fibrillae in the narrow middle part of the sensory 

 cells. When the middle part of the cell in the accessory retina is favor- 



