28 bulletin: museum of comparative zoology. 



pigmented part of the eye, and the eye would necessarily be regarded 

 as inverted. It need only be said that there is no evidence in my prep- 

 arations that nerve fibres and retinal cells are thus related, though 

 that is clearly the condition which Claus ('91), Hartog ('88) and 

 Richard ('91) had in mind. Therefore, if the relation between the 

 cells of the eye and the axis cylinders that arise from them is to be re- 

 garded as evidence that the eye is inverted or not, — that is, that the 

 recipient portions of the nerve fibre are or are not directed toward the 

 pigment and away from the exterior, — we must, at least in this case, 

 look upon such evidence as distinctly against the view that the median 

 eye in Copepoda is inverted. 



h. The NeurofihriUae. — But more direct evidence than that 

 hitherto presented is at hand relative to the character of the eye in 

 Eucalanus; it is based upon the relations existing between the end- 

 fibrillae of the nerves and the retinal cells. The character of the nerve 

 ending in the visual cells of Eucalanus has been investigated by Hesse 

 (:01, p. 349) in the course of his studies on the eyes of invertebrates. 

 He states that he was led to this investigation by a desire to know 

 whether or not the relationship believed to exist between the median 

 eyes of Crustacea and the eyes of flat worms, did not also extend to 

 the "lichtrecipierenden Theile der Sehzellen." He had ' previously 

 shown (Hesse, '97) that in Planaria and its allies there is in the visual 

 cells a "Stiftchensaum . . . . dessen einzelne Stiff chen nichts Anderes 

 sind als verdickte und vielleicht stofflich etwas veranderte Enden von 

 Neurofibrillen, Avelche von der Xervenfaser in ilie Sehzellen einstrah- 

 len " (Hesse :01, p. 350). With regard to the Copepoda he says (:01, 

 p. 350): "Die Untersuchung hatte das vermuthete Ergebnis: ich fand, 

 class das 'Stabchen' bei diesen Eormen ein Stiftchensaum ist." 

 His preparations of Eucalanus elongatus showed this condition the 

 most clearly, although the conditions in Eucalanus attenuatus and in 

 Calanus gracilis were practically the same. 



I have been unable to confirm, by my preparations, Hesse's state- 

 ments with regard to the presence of a Stiftchensaum in Eucalanus 

 elongatus. The iron-haematoxylin method following corrosive-acetic 

 fixation (which Hesse seems to have employed) is the least successful 

 of any that I have used in showing even the general relations between 

 axis cylinders and retinal cells. 



But any preparation will shoAV in the basal region of the retinal cells 

 an almost indistinguishable striation of the cytoplasm. This striated 

 appearance is seen to best advantage in vom Rath preparations (Plate 

 1, Figs. 5, 7, 9), though it is shown to some extent in sections stained 



