18 
G. H. Parker 
through cell 2 and reappears in most of the quarter-plates belonging 
to this cell, the other Clements of the retinula remaining almost en- 
tirely unaffected ; in other words, the Silver stain here, as in other 
cases, effects a given cell and the structure produced by it, but does 
not necessarily color neighboring cells. It was from seeing pre- 
parations such as this (Fig. 24) that I was led to regard the dorsal, 
ventral, and anterior half-plates as composed each of two quarter- 
plates, though I could never find a plane of Separation between them 
as between the pairs of half-plates. 
The fibres belonging to the other cells, 1, 5, and 6, in the 
section just mentioned are parallel to those of cell 2, as may be 
demonstrated in corresponding sections in which the fibres of all 
four cells are colored, and, as all dorsoventral plates agree in this 
respect, the general statement may be made that all the fibres in 
dorsoventral plates agree in having a common dorsoventral direction. 
In the anteroposterior plates the relation of the fibres to the 
cells and division-planes corresponds to that in the dorsoventral 
ones; i. e., the direction of the fibres in the former is anteroposte- 
rior, or at right angles to that in the latter. When a rhabdome in 
which the fibres are colored is cut so that the section includes 
parts of adjoining plates, the fibres appear to cross one another 
(Fig. 25) ; of course, in such cases the two sets lie at different levels. 
In longitudinal sections made parallel to one face of the rhab- 
dome, the fibres in one set of plates would be cut longitudinally, in 
the other transversely. Figure 23 represents such a section, in 
which, however, the fibres from only two cells are colored; those 
belonging to the cell on the left of the rhabdome are seen in longi- 
tudinal section and appear as thick lines; those in the alternating 
plates of the right half of the rhabdome are cut transversely and 
appear as dots. 
The fibres, as may be seen in the figures given, are always 
unbranched; of their two ends, one is buried in the retinular cell 
and the other usually reaches the division-plane between the two 
half-plates. Not infrequently fibres are seen that are not so long 
as this; I am uncertain whether these are really short ones, or of 
normal length but only partially stained (cf. Fig. 24). Occasionally 
some seem to pass through the division-plane and extend as rather 
delicate processes into the adjoining half-plate (Fig. 24); this I am 
inclined to regard as the result of the spreading of the Silver from 
the deeply colored fibres of one half-plate to a few in the adjoining 
