ESTERLY : EUCALANUS. 47 



practically the same in the two cases. Taking into consideration the 

 fact of the position of the retinal cells with reference to the hypodermis, 

 the lateral ocelli of the median eye of Eucalanus may be homologized 

 with the lateral eyes of the Pontellidae. The latter are, it is true, 

 more specialized, but were originally portions of the "nauplius" eye. 

 The conditions in Eucalanus show, I believe, the first steps in a proc- 

 ess by which the lateral ocelli (as represented in Pontella) have left 

 the ventral ectoderm of the body and the ventral ocellus of the trip- 

 artite eye, and have finally become both subepithelial and dorsal 

 in position. The ventral eye of such forms as Pontella (in the adult) 

 is the remaining (median) portion of the median eye, and not the 

 homologue of the entire tripartite median eye. Claus ('91, p. 24S) 

 based his conclusions upon the structure of the ventral eye of Pontella. 

 He found that it consists of a middle and two lateral portions and 

 therefore, in his opinion, corresponds to the median eye with its three 

 pigment cups and retinas. 



Zograf (:04), with whose work I am acquainted only from reviews, 

 assigns a later origin to the paired ocelli of the median eye than to 

 the ventral part, and considers that the three have become united 

 only secondarily. 



In all of his papers, Hesse has laid much stress upon the character 

 of the nerve endings in the visual cells. In his concluding discussion 

 (:02, p. 598) he distinguishes two sorts of visual cells on the basis of 

 the reci])ient parts: those with free endings of neurofibrillae, and 

 those with "Phaos-omes," the latter being by far the less numerous. I 

 have already mentioned the extent to which, in Hesse's opinion, the 

 free nerve endings occur in the form of a "Stiftchensaum." He 

 (Hesse, :02, p. 608) applies the term phaosome to intracellular bodies 

 in the visual cells of Naidae and Lumbricidae. "Die Ausdrticke, 

 welche bisher fiir diese imd iihnliche Gebilde gebraucht sind, wie 

 Vacuolen, Binnenkorper, Glaskorjjer, sind zu unbestimmt, oder 

 auch fiir andere, durchaus verschiedene Objekte in Gebrauch, so 

 dass ich sie lieber nicht gewahlt habe." If I understand his idea 

 correctly, he considers it possible that free nerve endings are found 

 in cells which possess phaosomes. "Jedenfalls ist zu vermuthen, 

 dass auch in den Sehzellen mit Phaosomen, wie in alien Zellen des 

 Nervensystems, Neurofibrillen vorhanden sind." "So lange diese 

 in ihrem Verhalten zu den Phaosomen nicht nachgewiesen sind, 

 muss jede Vermuthnug, ja sogar die Annahme, dass die Phaosomen- 

 zellen von denen mit freien Neurofibrillenenden grundsiitzlich ver- 

 -schieden seien, als jirovisorisch erscheinen "Die Verbreitung der 



