1886.) The Arthropod Eye. er ae | 867 
pigment, connective-tissue and nerve fibers. The latter grow out 
r; from the ganglion, the others are of mesoblastic origin, and force 
: their way into the cavity at about the time when the cells of its 
walls begin to elongate. The crystalline cone is plainly formed 
by the walls of the retinophora and these same cells can also be 
seen to elongate and unite to form the pedicel, thus clearly dem- 
~ Onstrating the truth of Patten’s position and the error in Gren- 
= acher’s conception of the rhabdom. I hope soon tq publish a 
À detailed account of my results with figures which will make clear 
~ all the points indicated above. 
nated pit shows conclusively that this organ could not have 
_ arisen from a confluence of ocelli, but must have had its origin 
from the division of a simple eye in some respects like that of a 
Spider. Farther, the close correspondence observable in the 
development of the eye of a spider and that of a crustacean, as 
outlined above, and the difference of both from that of Peripatus 
I took last year (Inter-relationships of Arthropods, this journal, 
XIX, pp. 560-567; and Embryology of Limulus, Quart. Jour. 
cros, Sci., xxv, pp. 52 1-576) that the group Tracheata is not 
a natural one, and that the spiders are far more closely related to 
the Crustacea than they are to the Hexapods, with which they 
are usually associated. 
E does not at leást conflict with another point I suggested in 
P ertpatus, in spite of its tracheæ, is not an Arthropod at all. To 
Sure it arises by an invagination, but so does that of cephalo- 
_ Pods and, in a modified way, those of vertebrates. We know 
: j almost nothi 
. but the almost perfect similarity shown between the eye of the 
__ TE Peripatus as figured by Balfour and that of the syllid worm 
2 ‘Autolytus as it is seen in my own preparations—a similarity ex- 
tending to almost every detail—renders it a not very rash step to 
Predict that invagination will be found to play a part in the devel- 
‘pment of the annelid eye as well, 
eget, 
and the ocelli of Hexapods, go far toward sustaining the position | 
_ At the same time the structure of the eye in the adult Peri- 
Paper in the American NATURALIST just quoted, z. e. that — 
ng of the development of the eyes of other groups, — 
This development of the compound eye from a single invagi- 
‘ig : 
