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 hvpodermis and to the 

 nerves are important in considering the phylogenetic position of the 

 median eve. 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 metlian eye of Crustacea "phylogeiie- 

 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 Plathehninthen gehort zweifellos die 

 Trochophoralarve, der wir wohl die Naupliuslarve zugesellen diirfen. 

 Von diesen Larven ist vielleicht iliese 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 liegen, 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 nauplius 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. I'inally, Zograf (:04), according to 

 his reviewers, looks upon the iui])aired eye as an organ that occurretl 

 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 eve of Eucalanus, which has been held to be a 



