42 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
verted, even through reversion, as Hesse (:02, p. 620 and 631 ff.) has 
maintained is the case among certain flatworms and the leeches. 
The relations of the cells of the eye to the hypodermis and to the 
nerves are important in considering the phylogenetic position of the 
median eye.’ Most, if not all, investigators have been inclined to 
refer the median eye to the pigment-spots on the apical plate of annelid 
larvae, and through these to the flatworms. Claus (’91, p. 260) states 
that the three optic cups of the median eye of Crustacea ‘‘phylogene- 
tisch vielleicht mit den Punktaugen an der Scheitelplatte von Anneli- 
den-larven in Beziehung zu bringen sind.” And Hesse (:02, p. 644) 
draws a similar comparison; the inverted pigment-cup type of ocellus 
is found in all the flatworms or is derived therefrom by reversion. 
“In die Verwandtschaft der Plathelminthen gehoért zweifellos die 
Trochophoralarve, der wir wohl die Naupliuslarve zugesellen diirfen. 
Von diesen Larven ist vielleicht diese Form der Sehorgane auf die 
fertigen Thiere iibergegangen: so finden wir sie bei niederen Anneli- 
den, und zwar meist dem Gehirn anliegend, wie sie bei der Larve in der 
Scheitelplatte legen, und bei den Medianaugen der Crustaceen ist es 
ja sicher, dass sie die persistierenden Naupliusaugen sind.” Hesse 
(:02, p. 647) also states that the median eye in Crustacea is nothing 
more than a structure inherited from ancestors probably like the flat- 
worms. And both Lang (88-94, p. 421) and Korschelt und Heider 
(90, p. 386) consider that the nauplius is referable to a trochophore 
larva. Crustacean characters are concealed (zuriickverlegen) in the 
nauplius, though the median eye is not mentioned as one of these 
characters. Lang is strongly of opinion that the nauphus larva does 
not represent the aucrestral crustacean form. ‘The latter is, in his 
opinion, to be sought among the worms, and the nauplius is to be 
regarded as a typical crustacean larva, which possesses many primi- 
tive characters of Crustacea. Finally, Zograf (:04), according to 
his reviewers, looks upon the unpaired eye as an organ that occurred 
in the primitive Crustacea, since it is present in the larvae or embryos 
of all Crustacea, and even persists in certain of the higher forms. 
Claus (61) proved its presence in the larva of malacostraca. (See 
also Hartog, ’88, and Balfour, ’80, p. 417 ff.) 
These references show the manifest tendency of investigators to 
consider the ‘‘nauplius eye” as a primitive one (Claus, 63, p. 44), 
and to base upon this, as well as other characters, the argument for 
the relationship between worm-like forms and the Crustacea. ’ 
I believe that the facts I have brought forward show that, as far as 
regards the median eye of Eucalanus, which has been held to be a 
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