OR ge ON eS ey 
ESTERLY: EUCALANUS. 39 
and nerves. ‘he relation of the latter to the cells is not the same as in 
the median eye, however. For there we have seen that, whether the 
“central cell” (pigment cell) or the basal plates are regarded as the 
pigment-bearing portions of the eye, the nerves leave the retinal cells 
from their Basi. ends, or that portion of the cell adjoining the pigmented 
part of the eye, whereas in an organ of Claus, the nerve leaves that 
portion of the periphery of the cell which is farthest removed from: the 
basal plate (Plate 2, Figs. 19, 20; Plate 3, Figs. 26, 29; Plate 5, 
Fig. 55). Consequently, if we follow consistently the cue pseiasion 
hitherto given of the relation between a sensory cell of an optic organ 
and its nerve fibre, the organs of Claus are to be regarded as bi-cellular, 
enverted eyes. In other words, the ends of the nerve fibrils are directed 
toward the bases of the sensory cells. But in the median eye, the 
light recipient portions of the optic nerves are directed toward the 
outer ends of the cells. 
III. Discussion. 
From the previous references to the literature bearing upon the 
subject, it has appeared that, with the exception of Grenacher (’79), 
all who have studied the median eye of Crustacea have either defi- 
nitely stated their belief in the inverted character of the retinal cells 
(Hesse, :01, :02; Claus, 91, Hartog, ’88; Richard, ’91), or, taking 
neutral ground upon this particular point, have felt that a close com- 
parison with the eyes of the flatworms was justifiable (Carriére, ’85; 
Lang, 88-94; Claus, 63). A quotation from Hesse (:02, p. 630) will 
put this matter concisely, and since it comes from one whose knowledge 
of the optic organs in invertebrates is unexcelled, it may be considered 
as representative. “Die invertirten Pigmentbecherocellen haben 
eine sehr weite Verbreitung. Alle Sehorgane, die wir bei den Plathel- 
minthen kennen, sind hierher zu eee also die Ocellen der Tur- 
bellarien, die x-f6rmigen Augenflecke der ’rematodenlarven, und 
die Ocellen der puecebildcten ektoparasitischen Tetcmiancde die 
Ocellen der een und wahrscheinlich auch diejenigen der 
Rotatorien. Ferner gehéren hierher mit grosser Wahrscheinlichkeit 
die Ocellen der Trochophoralarven und ahnlicher Larvenformen, 
sicher die Ocellen des Nauplius und die mit ihnen identischen Med- 
lanaugen vieler ausgebildeter Crustaceen....’’ From this point of 
view it may readily be seen how it is possible for such a statement as 
the following (Hesse, :02, p. 647) to be made: “Bei den Crustaceen 
