22 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
seems to me to be indicated by the innervation of the retina. The 
facts concerning the latter have been rather confused, if one considers 
all the accounts in the literature. In general the manner of innerva- 
tion has been looked upon as a factor in determining the phylogenetic 
relationship of the Copepoda. 
Grenacher was the first to determine the way in which the axis 
cylinders are related to the retinal cells. He says (Grenacher, ’79, 
p. 65) that the fibres of the optic nerve “are continuous with the inner, 
pointed ends of the cells,” meaning the ends nearer the pigment plate. 
He was able to follow the nerve fibres into the cells. 
Following Grenacher’s work, came that of Hartog (’88, p. 33), who 
found that in Cyclops the ocellus receives the nerve posteriorly at the 
outer surface, so that the optic elements are reversed as in the flat- 
worm Dendrocoelum. ‘The partition which separates the eye from the 
brain is “quite imperforate by nerves.” Further on (p. 34) he states 
that in both Cyclops and Calanus he followed a few fibres along the 
septum between the blocks of the lateral ocelli, and had positive evi- 
dence that such do not enter the “‘bacilli”’; they may end in the nuclei 
of the blocks or pass on to the frontal region. And in a footnote (p. 34) 
he describes the results of dissecting and sectioning the eye of Calanus 
in alcoholic specimens; he there found that “‘the lateral branches [of 
the optic nerve] unquestionably do not enter the inner ends of the 
bacilli”; he was unable to speak with certainty about the ventral eye. 
As already stated, Claus (’91) did not confirm Grenacher’s observa- 
tions as to the point at which the optic nerves leave the cells of the eye. 
Claus was evidently of opinion that the nerve leaves from the outer 
side of the visual cells and that the recipient ends of the fibrils are turned 
toward the pigment body, thus making the median eye an “‘inverses 
Becherauge.” He found this to be the case in the Cypridinidae, 
Branchiopoda, Cladocera and Argulidae and implies that it is so in 
the Copepoda and Cirripedia. 
Richard (’91, p. 208) also found that the retinal elements are “ren- 
versés comme dans les yeux marginaux des Pecten et dans celui des 
Vertebrés,” for the optic nerves do not enter the pigment mass, but 
pass to the dorsal margin of each simple eye and terminate at the 
surface. 
Other investigators are more or less inclined to consider the parts of 
the median eye as inverted. Schmeil (97, p. 30) accepts the state- 
ment that such is the case. Carriére (’85, p. 178) leaves the question 
open, but considers the resemblance of the eyes of Calanella (Kucala- 
nus) to those of Clepsine or Planaria ‘‘as unmistakable.” Lang 
