ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
417 
there is a turning backwards of the pallial complex (Bulla), and with 
the falling backwards of the visceral mass there is a dragging backwards 
of the heart, and further retreat of the pallial organs, with a diminution 
of the pallial cavity ( Philine ). When the shell becomes flattened out 
or rudimentary it ceases to exercise any distorting influence on the 
body, and the foot and mantle become the modifying factors, leading 
to characteristic variations. In the Nudibranchs the original bilateral 
symmetry of the Mollusc is apparently resumed, but the lost organs of 
the one side do not again reappear. The author thinks he sees indica- 
tions in the Tectibranchiata that there are two lines of development 
according to the relative preponderance of the mantle or foot. Judging 
from this evidence alone, we should presume that the cerata are neither 
the homologues of the mantle nor of the foot, but they may be the one 
or the other in different cases, and there is no reason why they should 
not sometimes be both. 
a. Cephalopoda. 
Retina of Cephalopods.* — Herr M. v. Lenhossek has studied the 
eyes of Sepia , Eledone , and other Cephalopods, using especially Golgi’s 
method. The optic cells are long narrow elements, palisade-like in 
their arrangement, extending vertically through the retina. Their 
inner ends or rods reach the homogeneous membrane which lines the 
cavity of the eye ; their proximal ends enter into relation with the optic 
fibres which are distributed from the posterior convex side. Only the 
rod projects into the epithelium, the nucleated protoplasmic part of the 
optic cell is separated from the epithelium by a limiting membrane. 
The distal end of the rod is pigmented and swollen like a club; the 
proximal end is a pigmented spindle, and between the spindles, above 
the limiting membrane, there are indifferent pigmented epithelial cells. 
Below the spindle is a clear portion — the Stabchensoclcel — slightly ex- 
panded at the level of the limiting membrane. Beneath this is the cell 
proper, which passes into an optic fibre. In short, the optic cells are 
true nerve-cells — the origins of the optic fibres. These grow out as 
processes of the cells centripetally to the optic lobe. 
Thus, contrasted with a Vertebrate eye, the Cephalopod eye has but 
one layer, divided into a dioptric and a nervous part. Or do the optic 
cells of the Cephalopod eye represent only the rods and cones of the 
Vertebrate eye, the other layers being displaced into the optic lobe ? To 
the fact that the rods of Invertebrate eyes are turned towards the cavity 
of the eye, while in Vertebrates they are towards the brain, the author 
does not attach great importance. The difference follows from the 
different mode of development. Starting from the epithelial sensory 
nerve-cells of the earthworm, von Lenhossek briefly sketches the possible 
evolution of the eye. 
Gigantic Cephalopod from Japan.f — Prof. K. Mitsukuri and Mr. S. 
Ikeda give an account of a gigantic Cephalopod which was caught in 
the Bay of Tatewama. They give a detailed account of this specimen, 
which appears to belong to the genus Architeuthis. In many respects 
the gigantic Cephalopod seen by Hilgendorf in Tokyo appears to agree 
* Zeitschr. f. wiss. Zool., lviii. (1894) pp. 636-60 (2 figs.). 
t Zool. Mag., vii. (1895) pp. 39-50. 
