80 The American Naturalist. (January, 
Formation of the Annelid Eye.—Our knowledge of the em- 
bryonic stages of the eyes of Annelids has been so scanty that the 
additions made by Ed. Beraneck® cannot be but welcome however 
little claim they may have to being exhaustive. 
The author has studied the. egg of the Alciopide, in the larva and 
adult and added to what had been previously made known by 
Kleinenberg and Greef. The eyes in this family of annelids, 
-it will be remembered, rank amongst the most complex and perfect of 
visual organs and are far larger and more specialized than those of i 
any other annelids. The structure is as follows; the optic vesicle is @ 
closed, a single layer of cells acting as cornea on the side next the thin 
epidermis and as retina elsewhere. Within the vesicle are the diop- = 
tric media: a spherical lens next the cornea, a very voluminous — 
vitreus body filling up the large vesicle and subdivided into an outer : 
part towards the retina and a major mass towards the lens, finally the 
rods that tip the retinal cells and line the vesicle except on the side of — 
the cornea. It is important to note that the eye is a closed vesicle not 
a cup ashas been claimed by Graber and denied by Graff and Carriere, 
Moreover this vesicle is a single layer of cells, hence the retina is 4 
single layer of cells, each having a long rod pointing towards the centre 
of the eye. In the adult there are no cells in the eye except those — 
that form the walls of the vesicle: neither lens nor vitreous body — 
presents any signs of cellular origin. The piginet of the retina is iD 
the cells that bear the rods, at the end whence springs the rod. 
It is thus obvious that this eye has no resemblance to the arthropod — 
eye: as the author points out in detail. a 
: 
| 
The formation of the eye is made out from sections of larve. The , 
= the eye isstill surrouned by numerous cells that gradually specialize 
as the cornea and retina. z 
- “Revue Suisse de Zoolögie. I. June 1893. 
