12 
G. H. Parker 
containing their four nuclei (Figs. 1 and 4, nl.con)\ secondly, a more 
elongated portion nearly uniform in calibre and constituting the cone 
(Fig. 1, con)\ thirdly, a still longer part tapering gradually from its 
distal to its proximal end and reaching nearly to the rhabdome 
(Figs. 1 and 6) ; and, lastly, a proximal portion in which the ends 
of the four cells, as separate fibres, pass around the rhabdome to 
terminate finally on the distal face of the basement membrane (Figs. 14, 
18, and 7, fbr.con). 
According to Szczawinska (91, pag. 542), who has followed 
Patten (86) rather closely, the cone-cells in Astacus do not end in 
fibres as described in the preceding paragraph, but are directly 
continuous with the rhabdome, which is formed, in fact, by an 
enlargement of their proximal ends. The fibres that I have mentioned 
as proximal portions of the cone-cells have been identified by 
Szczawinska (91, pag. 545), but she has interpreted them as processes 
from the distal retinular cells (cellules de l'enveloppe externe) and 
not from the cone-cells. There are, however, only two such cells 
in each ommatidium, not four, as she states, and thus the number 
of fibres does not agree with Ihe number of cells. Moreover, in 
sections from the distal end of the retinula (Fig. 14), it is easy to 
demonstrate not only the four fibres from the cone-cells (fbr.con)^ 
but also ,two fibres (fbr.dst) from the distal retinular cells. Since 
the connection of these fibres with their respective cells can be 
clearly shown in maceration-preparations as well as in serial sections, 
I believe that Szczawinska's interpretation of the four fibres is 
incorrect and that they really represent the proximal ends of the 
cone-cells. 
In a previous paper on the eye in Homarus (Parker, 91, pag. 545), 
I tried to show that the rhabdome and cone-cells were separate struc- 
tures, as first maintained by Max Schultze (68), and that the fibres from 
the latter terminated on the basement membrane. This conclusion has 
been fully confirmed by Viallanes (92, pag. 361) in his account of 
the eye in Palinurus^ and Patten (90, pag. 354) also now accepts it, 
though among recent investigators he was the first and most active 
to declare for the continuity of rhabdome and cone-cells. In view 
of these facts, it seems to me that the idea of continuity must be 
abandoned and that the cone-cells and the rhabdome must be regarded 
as separate structures. 
Of the distal retinular cells surrounding the cone, one is 
dorsal and one ventral in position as shown by their nuclei (Fig. 5, 
