40 
and compound eye in insects. The former 
is believed to be of little use except merely 
in perceiving the intensity of light. The 
latter includes two radically different eyes : 
a true compound eye in the brachycerous 
diptera, the lepidoptera, orthoptera, and 
coleoptera ; and the aggregate eye in the 
hymenoptera, nematocerous diptera, hem- 
iptera, and many coleoptera. The de- 
tails of structure are of course too complex 
to admit of an intelligible abstract. Miil- 
ler’s, or the ‘‘ mosaic” theory of vision is 
regarded as the most probable, and Mr. 
Lowne’s remarks on the sharpness of insect 
vision are most interesting. -Aeschna, Ves- 
pa, and Bombus are supposed to see an 
object 20 feet distant, in the same detail as 
man would do at 160 feet, and this when 
the object is in the line of greatest sharp- 
ness of vision. Tabanus sees in the same 
way at 20 to 360; Syrphus, 20 to 1200, 
Noctua, 20 to 2400, and Tipula, 20 to 
4800. In Mr. Lowne’s view then, the in- 
sect eye is far from sharp-sigh‘ed, and if he 
is correct it would seem difficult to explain 
the delicate patterns of coloration by sexual 
selection, as has generally been done. 
Prof. Grenacher’s work leads Dr. V. 
Graber * to publish an important paper on 
the simple eye of the Tracheata, especially 
referring to spiders and myriapods, the lat- 
ter group having been neglected by Grena- 
cher. 
stemma, shows the pore canals as well as 
the lamination of the rest of the cuticula. 
The crystalline body (hypoderm) is sepa- 
rated from the retina by a lamella, which is 
the extension of the inner cuticular mem- 
brane which underlies the hypoderm. 
56 Arch. Mik. Anat., v. 17, p. 58. 
57 Morphol. Jahrbuch, v. 4, p. 279. 
The cornea of the simple eye or 
PSYCHE. 
This fact speaks against the hypodermic 
origin of the retina. The inner cuticula 
also extends downwards, clothing the whole 
retinal elements (sclera). The retinal seg- 
ments are not single cells like those of the 
facetted eye, but show a basal ganglionic 
cell and a nucleated distal cylinder. The 
axial rod of the cylinder in Buthus seems 
to be a direct continuation of the ganglion 
cell, and so of an optic fibre. The stemma 
of Buthus is nota single optic element, but 
really a pentamerous compound eye. 
Graber also points out the similarity be- 
tween the auditory elements (in Acrid- 
ium) and the optic elements are described. 
Mr. Anton Stecker® finds that in the 
pseudo-scorpion genus Chernes, which is 
usually eyeless, some specimens possess 
In Chernes cimicoides 
specimens were found with transparent 
rudimentary eyes. 
spots in the position of the eyes in chilo- 
pods. To these spots an optic nerve pro- 
ceeds from the optie lobes, but there is no 
About 33 
per cent. of the specimens were thus semi- 
eyed. The rest were totally blind, and 
wanted the optic nerves. The former class 
were offspring of seeing parents, while if 
either parent was sightless, the young were 
always so. With these most interesting 
discoveries, is added the fact that the optie 
nerve seems to send many of its fibres to 
the connective tissue under the epiderm, 
thus assuming another function. 
Oscar Schmidt * in a short paper on the 
crystalline cone in arthropoda, discusses the 
mosaic theory of sight. His observations 
were mostly on the crustacea, a single par- 
agraph refering to Dyticus, in the eye of 
trace of the crystalline rods. 
58 Zeitschr. wiss. Zool. v. 30, Suppl., p. 1. 
