esterly: eucalanus. 43 



tA^^ical nauplius eye, a comparison of it with any of the typical eyes 

 found among flatworms or the lower annelids is not justified. Con- 

 sequently, I do not feel that the conclusion of Hesse (:02, p. 644) 

 already quoted is warranted at present, especially in view of the com- 

 plete absence of embryological facts to support his contention. 



But that there are light-recipient organs among Crustacea which are 

 in every way justly comparable to those of the lower annelids and the 

 flatworms, is shown, I believe, by the facts already brought forward 

 concerning the structure of the organs of Claus, and by comparative 

 evidence derived from the group of worms. 



Von Graff ('82, p. 115) has shown that in the rhabdocoele flat- 

 worms, the pigmented and lens-bearing eyes are situated directly 

 upon the brain, and Carriere ('85, p. 25) states that eyes to the number 

 of two or four occur inside the brain. 



The investigations of Hesse ('96, p. 404) led him to conclude that 

 the structures which function as eyes in the lyumbricidae are located 

 in the brain as well as in the epidermis. Among the Capitellidae, 

 also, Hesse ('99) has shown that the cup eyes are found both in the 

 brain and in the epidermis, and this holds for many other forms of 

 the limicolous annelids. The position of the organs of Claus, how- 

 ever, has a deeper significance, if we look upon them as subepithelial. 

 According to Hesse (:02, p. 620) the eyes of Plathelminthes, the cup 

 eyes of Capitellidae (in part), and of many polychaete annelids are 

 subepithelial, as well as the median eye in Crustacea. But it appears 

 that only the lateral portions of the nauplius eye can be regarded as 

 ■subepithelial, while the entire organ of Claus must be so regarded. 

 Since the organs of Claus lie entirely within the brain, which has lost 

 all connection with the ectoderm (being separated from it by a thick 

 membrane), they are neither epithelial nor intra-epithelial as these 

 terms have been defined. 



In 'position, then, the organs of Claus may be considered as homol- 

 ogous with the simpler eyes found among the flatworms and certain 

 groups of the annehds. Hesse ('99, p. 477) is of opinion that the 

 *'Becherauge" is of the same form as that generally distributed 

 through the Plathelminthes, the type being found in Planaria torva; 

 also (p. 483) that the goblet eyes in the lower annelids are essentially 

 like those of the planarians. 



It is my belief that the facts previously presented warrant us in 

 extending this statement of Hesse to the organs of Claus found in the 

 brain of Eucalanus. I have shown that the axis cylinders which pass 

 from the visual cells of the median eve to the brain, leave the basal 



