is asserted above but not demonstrated, though the course of the mesencephalic root of the trigeminus would support such a view. This view hardly furnishes an explanation of the peculiar position of REISSNER'S fiber.

O. S. 8.

Parker, G. H. The Phototropism of the Mourning-Cloak Butterfly Vanessa antiopa Linn. Art. XXIII, pp. 453-569, pl. 33.

V. antiopa orients itself in sunlight with its head away from the sun and so that a straight stick held vertically at an appropriate point casts a shadow that falls exactly on the length of the butterfly's body. So invariably is the head directed away from the sun that when resting on tree trunks the butterflies face toward the foot of the tree. If the surface on which it rests "is perpendicular to the sun's rays the in. sect settles without reference to the direction of the rays." Nevertheless, "V. antiopa creeps and flies toward a source of light, that is, it is positively phototropic in its locomotor responses." This positive phototropism of flight or other locomotion and negative phototropism in rest are otherwise not unknown.

Now the author finds that the resting animal keeps its wings spread in sunlight and that the position of negative orientation most fully exposes the wings to light and makes the insect conspicuous. The habit is therefore probably a means of bringing males and females together. Furthermore, it is the eyes which govern the reaction, since any part of the body except the head may be shaded without disturbing the animal, which, however, flies away if the head is shaded. This observation is confirmed by various experiments on animals of which the eyes have been painted over. If one eye is blackened, that side of the insect keeps in motion and the body moves "in a circle, with the unaffected eye toward the center." If both eyes are blackened, the insect does not come to rest, but flies upward, showing a negative geotropism which is readily verified on normal individuals in a perfectly dark room.

V. antiopa discriminates little, if at all, between different intensities, much more between lights of different area. It "remains in flight near the ground" and, although in locomotion positively photropic, does not fly upward toward the sun, "because it reacts positively to large patches of bright sunlight rather than to small ones, even though the latter, as in the case of the sun, may be much more intense." These reactions are probably based on retinal images which the insect gets. If the sun is clouded over the animals fold their wings.

The "heat-rays" of sunlight seem not to influence the reactions, but an actual change of temperature of the air is effective. A marked de

crease in temperature, as at night-fall, independent of any decrease in light, causes the insets to settle down; and it is probably the daily changes of temperature which make V. antiopa retreat into hidingplaces at night and emerge in the morning.

It is not true, as has been paradoxically alleged, "that moths, which avoid daylight, fly into a flame at night, while butterflies, which fly by day, do not possess this fatal instinct." Butterflies also fly into a flame. The author does not confirm the hypotheses put forward by LOEB and by DAVENPORT in order to explain this supposed paradox.

E. B. H.

Hyde, Ida H. The Nerve Distribution in the Eye of Pecten Irradians. Art. XXIV, ', pp. 473-482, pl. 34.

The application of improved methods in histological research to the eye of Pecten indicates, according to the findings of Dr. HYDE, that the descriptions of this organ given by PATTEN, HENSEN and others are not entirely reliable.

A brief but clear description of the histology of the organ is given, and the author then turns to a more detailed consideration of the nerve supply and of the retinal elements. The main conclusions of the paper are thus stated: 1. The rods are not, as was formerly supposed, innervated by fibers from at least three series of nerves. "2. The socalled retinophorae are not the visual sensory cells whose peripheral fibers form the basal optic nerve, but they are the supporting cells of the median layer of the retina. 3. The inner ganglionic cells do not connect with the side branch of the optic nerve, but are the nervecells of the bipolar nerve elements. 4. The outer ganglionic cells form a single layer whose inner fibers are disposed in a special reticular structure in the retina and whose outer fibers make direct connection with the side branch of the optic nerve."

The author believes that the visual apparatus of the retina is composed of afferent and efferent neurones, and that the rods are true peripheral visual neurones.

The text is accompanied by an excellent plate which gives the general histology of the eye in one figure, and in others the details of structure of the retinal elements, together with their ganglionic connections.

R. M. Y.