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, lulus, and Glomeris 

 (Grenacher, '80, Figs. 9, 11, 13) — has also been confirmed by Lan- 

 kester and Bourne ('83, Figs. 2, 4, 7, 11) for Scorpionidse 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 

 (PI. II, Figs. 10, 11, and PI. 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 



