ESTERLY: EUCALANUS. 51: 
lar and somewhat beaded and branched; each terminates in a club- 
shaped enlargement. 
7. Consequently the character of the nerve-ending cannot be 
regarded as similar to that in the visual cells of worms, as Hesse has 
maintained. 
8. The cells of the median eye are not of the inverted type com- 
monly found among flat-worms and polychaetes. ‘Therefore the 
median eye is not to be regarded on this character as a structure 
inherited from worm-like ancestors. 
9. The ‘interior bodies” and neurofibrillae seem to be struc- 
turally continuous. Their functional interrelationship is therefore 
probable. 
10. The ventral division of the median eye is simply a thickening 
of the hypodermis of the body, and has retained, in the adult, its 
original position. ‘The lateral divisions of the eye have lost all except 
a very slight connection with the hypodermis. ‘The ventral division 
is in position epithelial; the lateral divisions are, in effect, subepithelial. 
11. These relations are interpreted as evidence that the lateral 
ocelli of the median eye of Eucalanus are homologous with the lens 
eyes of the Pontellidae. The ventral ocellus in Eucalanus corre- 
sponds to the ventral eye of Pontella. 
12. The organ of Claus is to be regarded as a bicellular, inverted 
eye. These organs are located symmetrically in the brain. 
13. Each cell of an organ of Claus possesses a basal plate and 
“interior bodies.” These structures are in every respect similar to: 
those found in the cells of the median eye. 
14. The nerves from the organs of Claus do not pass through the 
basal plates, but leave the periphery of the cell at a point which is 
opposite to the basal plate. In comparison with the retinal cells, 
these are consequently inverted. 
_ 15. In position the organs of Claus are subepithelial, and since 
they lie in the brain as well, they are strictly comparable to the in- 
verted pigmented ocelli of certain worms. 
16. Consequently, it is believed that if a relationship between the 
Copepoda and the groups of the worms is to be sought on the basis 
of the structure of the optic organs, it must be through the organs of 
Claus and not through the “‘ median eye.” Heretofore the median 
eye has generally been regarded as inverted, and on this character 
likened to the eyes of flatworms, which present that condition; but the: 
median eye of Eucalanus gives no support to that view. 
