Miscellaneous. 483 



The cavity of the ocellus is occupied by cells belonging to two 

 different types, besides a few little cellular elements applied against 

 the cornea, oven in the centre of its inner face. 



Tlie first, the Jlaarzellen of Grenadier, which are elongated and 

 of relatively little thickness and pigmented, form, by attaching 

 themselves by their large faces, a hollow cylinder, which separates 

 the cornea from the true retina. They terminate on the inner side 

 in delicate cilia, which, in my sections, do not appear with the 

 regularity which Greiiacher's figures ascribe to them, but are found 

 adhering together in irregular pencils. May these ciliated elements 

 be " giant " recipient cells similar to those w^hich Patten has 

 described in the larva of Acilius, and of which the altered rods 

 •would no longer be represented, in the preparations of Grenadier 

 and myself, except by tibrilkio running at right angles to the direc- 

 tion of the retinidium? I cannot admit this explanation, for the 

 •way in which these ciliated cells and the true retinal cells res})ec- 

 tively behave towards fixing reagents forces me to conclude that 

 these two kinds of elements have not the same morphological 

 significance. 



The bottom of the optic cup is occupied by some twenty retinal 

 cells, which Grenacher says he has been unable to observe in 

 their entirety except in exceptional cases. Each of these cells 

 presents a basal portion enclosing the nucleus, some pigment- 

 granules, and, in connexion with a nerve-fibre and a terminal 

 segment, Grenacher's rod, which is clearly transversely striated. In 

 certain favourable sections I have determined the presence, between 

 the striated segments of the adjoining cells, of elongated elements, 

 presenting the same appearance as the lateral rods of the retinal 

 cells of the larvae of Acilius. Sometimes, in transverse sections, I 

 have observed in the centre of the meshes of the plexus formed by 

 the section of the external segments, a corpuscle of special refractile 

 power, which I could only regard as the section of the axial nerve- 

 fibre of each cell. Do the transverse striations of the terminal 

 segment correspond to the fibrilloe of a retinidium, similar to that 

 which Patten describes generally in the terminal segments of the 

 retinophores ? This is a problem which the extreme minuteness of 

 the elements observed does not permit me to solve. 



The pigment-granules of the ciliated and rod-cells occupy a more 

 or less extended zone, according as the ocelli have been fixed in 

 sunlight or in shade. 



I would observe in conclusion that the appearance of certain of 

 my preparations resembling Graber's figure explains to me the error 

 of interpretation perpetrated by this observer, due to a rapid exami- 

 nation, with a preconceived idea, of sections which were not suffi- 

 ciently thin. — Comptes Eendiis, tome cxiii. no. 1 (6 juillet, 1891), 

 pp. 43-45. 



