ANATOMY AN t) PHYSIOLOGY. Moll. 39 
cell is a tapering conical rod passing through it and entering the gang- 
lionic layer. There are secondary concave lenses at the upper ends of 
the facets to counteract the main lenses, which are too powerful for use 
in air. 0. damelii does not retract its eyes on the close approach of 
foreign bodies, which may indicate that it is far-sighted; Lendenfeld. 
In Pterotrachea the eye has, roughly speaking, the form of a cylinder, 
the hinder portion of which has been compressed from above downwards. 
The hindmost extremity being constituted by a curved boat-shaped 
appendage, into which the optic nerve passos. Tho cornea is largo and 
spheroidal, but always destroyed in removing the organ. Pigment has a 
remarkable distribution ; a broad band (broader dorsally than ventrally) 
with curved margius passes round the eye, and from its lack of pigment 
has received the name “ Fenster a darker stria runs along its centre. 
The pigmented posterior part is separated from the remainder by a dis- 
tinct ridge (costa) on the inner surface. 
The capsule of the eye consists of a structureless cuticle of moderate 
thickness, the interior being lined with columnar epithelial cells of varying 
lengths. The retina (1) occupies the posterior boat -shaped portion of the 
eye, and is not to be regarded as made up of different histological layers, 
but of one layer, whose elements may be distinguished into pedestals 
and rods, the former outside, the latter inside a delicate limiting mem- 
brane. (2) There is no reason to refer the fibrillar contents of the 
nucleated section of the retinal cells to a breaking up into nerve fibres, 
but rather to a formation of “ radiculse ” for fixation to the cuticle. 
(3) The length of the striated pedestals is determined by the height 
of their insertion iuto tho rods. (4) Since a number of pedestals are 
connected with each rod, these, like the rhabd<*ms of Arthropoda and 
Cephalopoda , are to be regarded as composite, but the components are 
disposed one above another, not side by side. Their striation is due to a 
simple laminar texture. (5) The rods are arranged in longitudinal rows, 
parallel throughout the whole retina, which (6) is divided into dorsal and 
ventral halves by a slit. (7) The retina is innervated by a layer of fibres 
running under the basal ends of its cells ; its dorsal portion contains 
small ganglion cells. (8) The structureless membrana limitans, between 
the retina and vitreous, gives off fibres which penetrate between the rows 
of rods. (9) The nervous fibres pass forwards, and can be followed to 
distinct epithelial processes in the region of the costa ; they seem to pass 
into large cells surrounded by pigment, whose function is doubtful. 
An account of the function of the various parts, and a comparison of 
the organ with that of other Cephalopliora is added ; Grenacher. 
Sepice deprived of eyes swim in the usual way, but more slowly ; when 
the otocyst is removed, either with or without the eye, this power is no 
longer retained, the animal losing control over its actions. These experi- 
ments are compared with those of Flourens on rabbits ; DelAge. 
9. Generative Organs. 
The penis of Agriolimax maculatus , from Samarcand, possesses a firmly 
attached oval calcareous extremity with a double spur ; this supports the 
