ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
293 
There are, he says, processes of metabolism of which a chemical account 
can be given, but this is not true of the adaptive power of protoplasm, 
of its power of adjustment to new conditions, of the peculiar striving 
of living material towards a maximum of stability. Perhaps, as Prof. 
Mach says, our chemical ideas may in time deepen and broaden so as 
to include the phenomena of organic growth ; but this is not true as yet. 
Organs of Sight in Amphioxus.* — Dr. R. Hesse gives an account 
of his investigations on the pigment-spots in the spinal cord of im- 
pliioxus. He found these spots grouped together in a definite order 
corresponding obviously to the segmentation. Each individual pigment 
spot was cup-shaped, and contained a cell, one portion of which filled 
the hollow of the pigment-spot, while the other, containing the nucleus, 
was prolonged into a nerve, which could be traced for some distance 
among the fibres of the spinal cord. These organs closely resemble 
in structure the cup-eyes of Planaria torva. They lie on each side of, 
and below the central canal of the spinal cord, beginning in the third 
muscle segment, where there are only two on each side. From the 
fourth segment onwards there may be as many as twenty-five such cup- 
eyes grouped on each side, but from the middle of the body they decrease 
rapidly in number, and in the posterior segments they may be entirely 
wanting. Those on the right side lie about half the length of a 
segment behind those on the left. The cup-eyes lying underneath the 
central canal have their openings directed downwards ; those on each 
side have the openings directed upwards, but while the former are 
symmetrical in structure, the latter have one wall of the cup higher 
than the other — on the right side the inner, on the left the outer wall, 
so that the organ is turned towards the right. There is, however, not 
sufficient evidence to prove a connection between this arrangement and 
the animal’s habit of lying on the right side. Those underneath the 
central canal are probably functional when the lancelet lies on its back 
in the sand. 
Dr. Hesse’s physiological experiments yielded results similar in 
the main to those of Nagel, and corroborated his morphological in- 
vestigations. It might be suggested that “ cup-eye ” is too big a name 
for these little spots. 
Origin of Corpus Callosum.j — Dr. G. Elliot Smith has studied the 
brain in Percimeles nasuta , in the bat Nyctophilus , and other forms. 
£ - The great feature which far more than any other distinguishes the 
mammalian brain from that of all submammalia is the possession of 
a definite pallium — distinct alike in its histological features and its 
morphological relations — giving rise to a definite internal capsule of 
projection-fibres, and well-defined and fully- medullated commissural 
fibres. At first, in the Monotremata and Marsupialia, this pallium (like 
the parent mass of the basal ganglion from which it appears to have 
sprung) is united to its homologue of the opposite hemisphere by means 
of the ‘ commissura ventralis’ — ‘the commissure of the cerebral hemi- 
sphere ’ par excellence. 
“ But the rapid growth in extent and complexity of this general 
* Zeitschr. f. wiss. Zool., lxiii. (1S98) pp. 456-62 (1 pi.). 
t Trans. Linn. Soc. (Zool.), vii. (1897) pp. 47-69 (2 pis. and 8 figs.). 
