40 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
sind die Medianaugen nichts Anderes als die iibrig gebliebenen 
Naupliusaugen, die eine Erbschaft von wahrscheinlich  plathel- 
minthenartigen Vorfahren darstellen.” 
The essential point in all these comparisons is the inverted character 
-of the retinal cells of the median eye; it is maintained that the axis 
cylinders, which are made up by the union of neurofibrillae from 
within the cells, leave the cells from that part which is directed away 
from the pigment. But, if the eye of Eucalanus may be taken as the 
type of the so-called persisting nauplius eye, such a comparison as 
that instituted by Hesse must fail, as well as the conclusions deduced 
from it. Hesse himself (:01, p. 350) has considered the median eye 
in Eucalanus as of typical form, as did Grenacher (79, p. 63) and 
others who followed him (Carriére, ’85; Lang, 88-94); in the ab- 
sence of trustworthy evidence to the contrary, it seems to me that 
such a median eye may fairly be taken as representing the general 
form of the tripartite eye as found among Crustacea. At any rate, 
the median eye is a more characteristic structure in the Copepoda 
than in any other group, and, among the Copepoda, the eye of 
Eucalanus has been more adequately studied than that of any other 
genus. 
But so far, then, as my observations extend, there is no evidence 
from the manner of innervation of the median eye that it is of the 
inverted type. For, as Beer (:01, p. 12) has said of the uninverted 
eye “das Licht unter den gewoéhnlichen Bedingungen erst die Photir- 
zelle, dann den Opticusabgang trifft.” 
The median eye of Crustacea has been placed in the same class 
with those of the flat-worms, and of many annelids, on account of its 
position as regards the epithelium. Hesse (:02, p. 620), in a table 
giving the results of his investigations, includes the median eye of 
Crustacea among those whose visual-cells are subepithelial. This 
term is defined (Hesse, :02, p. 619) as follows: ‘‘Wenn dieser gleiche 
Vorgang, der eine urspriinglich epitheliale Sehzelle zur intraepithe- 
lialen werden lisst, noch weiter fortschreitet, so verlisst die Sehzelle 
den Bereich des Epithels vollkommen: sie wird zur subepithelialen 
Sehzelle.” Claus (91, p. 260) is also of the opinion that the median 
eye as a whole is separate from the hypodermis. I believe my results 
prove that only the paired portions of the median eye can be regarded 
as subepithelial in the sense in which Hesse has used the term. 
There is very little indication in the adult condition that the lateral 
eyes are a part of the general ectoderm of the body; consequently 
they cannot belong to Hesse’s class of epithelial eyes, and there is 
