230 Dr. H. Dor on Vision in the Arthropoda, 
ornata, costellis in medio nullis, lineolis concentricis incrementi 
striolata; margine ventrali crenulato. 
Hab. Mino-Sima; 63 fathoms. 
A small species, very nearly similar in form to Crenella, but 
with the middle of the valves: plain. 
Nagasaki, July 10, 1861, 
- XXVIL.—On Vision in the Arthropoda. By Dr. H. Dor*. - 
Compounp eyes occur in nearly all Crustacea, in all winged and 
some apterous insects, and even in the aquatic larvee of the Neu- 
roptera, and in the larvee of the Hemiptera. They are two in 
number, and form a segment of a sphere; and each is composed 
of an agglomeration of more simple organs, of which the number 
varies almost infinitely (from 50 to 25,000 in a single eye). The 
facets formed by the single eyes resemble the cells of a honey- 
comb: they are usually hexagonal, but sometimes pentagonal, 
rectangular, or irregular; and these various forms may be met 
with in the same eye. 
On making an antero-posterior section of the eye, each facet 
is found to correspond with a more or less lenticular organ, 
exactly resembling in some species the crystalline lens of the 
Vertebrata. This has been called the cornea. Behind it is the 
crystalline body, a transparent and strongly refractive cone, en- 
closed in a cupuliform envelope, which is also transparent and 
is perfectly continuous with the nervous fibre. The union of all 
the nervous fibres, which in their course almost constantly pre- 
sent a dilatation and afterwards traverse several masses of gan- 
glionic cells, forms the optic ganglion. The spaces between 
the different nervous fibres are filled up with a dark pigment. ~ 
The author gives a summary of the different views put forward 
by writers on the mechanism of vision in the Arthropoda. Cu- 
vier supposed that the nervous filaments, although each corre- 
sponding to a facet, lost themselves in the layer of pigment ; and 
he found it difficult to understand how impressions could be pro- 
duced upon them through this opake matter. Marcel de Serres 
did not recognize the conical crystalline bodies, the discovery of 
which is due to Treviranus (Verm. Schriften, i. p. 152), who, 
however, did not perceive their importance. According to him, 
the compound eyes act like a convex mirror, upon which objects 
are reproduced enlarged, the entire cornea reflecting images of 
distant objects, and each facet those of neighbouring objects. 
* Abstract from the ‘Bibliothéque Universelle,’ 1861, “Archives des 
Sciences Physiques et Naturelles,”’ p. 328. ; ; 
