esterly: eucalanus. 51 



lar and somewhat beaded and branched; each terminates in a chib- 

 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 hiceUuIar, 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 peri])hery 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 relationshi]) between the 

 Copepoda and the groups of the M^orms 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 jiresent that condition; but the 

 median eye of Eucalanus gives no support to that view. 



