84 BULLETIN OF THE 
The method of connection between retinal cells and optic-nerve fibres 
is a fact upon which Grenacher has placed great importance, since upon 
it depends largely, in his opinion, the interpretation given to the func- 
tional value of the individual elements of the retina. According to 
Grenacher’s investigations (’79 and ’80) the posterior (deep) end of each 
cell of the retina (in the “Stemma”) is prolonged into a single nerve- 
fibre, the optic nerve being composed of a bundle of such fibres, pre- 
sumably as numerous as the retinal elements. This condition — espe- 
cially well marked in Dytiscus, in the posterior dorsal eyes of Epeira 
(Grenacher, ’79, Figs. 1, 18, 20), in Lithobius, Iulus, and Glomeris 
(Grenacher, ’80, Figs. 9, 11, 13) —has also been confirmed by Lan- 
kester and Bourne (’83, Figs. 2, 4, 7, 11) for Scorpionide and other 
Arthropods. 
Without being prepared to question the accuracy of the observations 
of these authors in the cases cited, I am of opinion that there are suffi- 
cient reasons for not accepting as universal this mode of union between 
retinal cells and optic-nerve filaments. I do not wish to be understood 
as opposing the idea of the independent communication of the elements 
of the retina with the nerve-centre, but only as claiming that generali- 
zations as to the manner of union between retinal elements and optic- 
nerve fibres cannot be as quickly and safely drawn as might be inferred 
from previous writers. 
The nature of the optic-nerve connection in the anterior eye of Epeira as 
described and figured by Grenacher (’79, p. 44, Fig. 18, A) is in itself suffi- 
cient to raise doubts concerning the universality of the method claimed 
by him ; viz. a direct prolongation of the (ultimately) posterior ends of 
the retinal cells. Grenacher says that the peripheral fibres of the optic 
nerve are continued without sharp limitation directly into the neighbor- 
ing (“ herantretenden ”) retina-cells ; but the inner [axial] fibres enter 
into the interior of the retina, where they divide into two bundles, —a 
smaller dorsal, and a larger ventral, — which then spread out in single 
fibres, which in turn join the ends of the corresponding [retinal] cells. 
That which seems to me unwarranted in his conclusions is, that the axial 
fibres are joined to the ends of the retinal cells. It is not quite clear 
from the figure cited how this union could be easily effected. The same 
feature, but in a more marked degree, is also shown in Mr. Locy’s sec- 
tions of the anterior median eyes of Agelena a few days after hatching 
(Pl. II, Figs. 10, 11, and Pl. V, Figs. 23, 24), and in the adult eyes (an- 
terior median) of Theridium tepidariorum, C.K., which I have examined. 
Grenacher himself called attention to a want of symmetry in the eyes 
