a LPO OS 
€ 
ESTERLY: EUCALANUS. 43 
typical 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 Carriére (’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 Lumbricidae 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 subepithelval. 
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 le 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 annelids. 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 a 483) that the goblet eyes in the low er annelids are essentially 
like those of the planarians. 
It is my belief that the tacts 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 eye to the brain, leave the basal 
