SOOPELOIDS. 
921 
transformation and dissolution of the gland-cells, which 
are afterwards ejected through that end of the tube 
which opens into the hollow. 
From this comparatively simple structure, which 
as yet reminds us of slime-glands of ihe skin, the first 
step to higher differentiation is that, as the sac deepens 
more and more, its inner (bottom) part is separated by 
a constriction of the wall and becomes spherical in 
shape, while the outer part remains more or less re- 
gularly cup-shaped, a rotation-paraboloid with cir- 
cular mouth, in which case the axis is vertical to the 
surface of the body (fig. 231), or elliptical and more 
or less elongated", in which case the axis is obliquely 
set. Throughout the wall of the organ, within the 
layer of pigment, lies an extremely thin, but power- 
fully refractive membrane (m), which even extends over 
the mouth of the organ, where we also find a double 
membrane, consisting of an inner, cellular leaf ( d ) and 
an outer, structureless one (c) explained as a kind of 
lens, and situated within the thin, structureless epi- 
dermis ( b ), which has been compared to a cornea. The 
internal structure is otherwise essentially the same as 
in the simpler luminous spots — though both connective 
tissue and nervous elements enter more plentifully into 
its composition — but the shining mass (/c) here lies 
as a more or less lens-shaped body in the annular 
constriction between the spherical (inner) and cup- 
shaped parts of the organ, forming a disk between 
these two parts but itself divided into two parts (Jc 
and 1) by a thin membrane, which is distended like 
a diaphragm right in the constriction. To this disk 
run the extreme ramifications of the spinal nerve (n) 
Fig. 231. A: Section of a compound luminous spot in Astronesthes niger, X 100. After Lendenfeld. 
I, cornea-like, transparent part of skin over the organ; c, transparent membrane outside the lens-shaped body d; e, gland-tubes of the sphe- 
rical part; /, pigment layers; g and g. pigment coating of the outer and inner parts of the luminous body; h, gland-tubes in the outer part 
of the luminous body; Jc, granular mass and cells, inner part; l, outer part; m , shining membrane within the pigment layer; n, nervous cells. 
Fig 231. B: Diagrammatic section of the luminous spot represented in fig. A, showing the reflection and refraction of the rays 
of light in the luminous spot. After Lendenfeld. 
a i a 4 ar, d h & 4 , rays of light emitted from the central part (1c) of the luminous spot and reflected in the lower, spherical part of the 
same; Cj c 3 , dy d 3 , — e 3 , and fy — f 3 , rays of light from the same source, emitted in a centrifugal direction, reflected from the sides of 
the outer, parabolic portion of the organ, and refracted by passing through the cornea-like layer (g); xxy, axis of the optical system; 
Q , cornea; h, shining tissue of the outer, parabolic part; i, glands of the inner, spherical part. 
See for example the upper spots in our figure of Argyropelecus Olfersii. 
