676 JUSTUS CARRIERB. 



Among the matrix-cells of the cribriform basal membrane, 

 being there proportionately thick, numerous trachese ramify. 

 The thicker trunks of these are placed between the matrix-cells 

 and the ganglion layer lying below it. 



No more about the optic and light-perceiving part of the 

 eye. Behind it lies the ganglion apparatus which shows in 

 Musca a typical, but, as it seems, not very frequent con- 

 struction, the peripheral ganglion-opticum being spread out 

 close to the eye as a plane. 



Out of the central part of the brain passes a long and narrow 

 string of nerve-fibres through an interposed ganglion layer 

 into the central opticus-ganglion (13), radiating in it towards 

 all sides. 



This ganglion forms a cone turned with the point outwards, 

 with the concave base inwards to the brain. The inside of the 

 cone consists of several concentric layers of " Punktsubstanz " 

 (to employ Leydig's expression), which are connected together 

 by a great number of narrow granular strips, while the mantle of 

 the cone is formed by the ganglion-cells or the nuclei of them.^ 



(The subtler construction of the ganglion can only be 

 indicated in the Plate, because of the small size of the drawing, 

 and has also been sufficiently illustrated by Berger, ' Arbeiten 

 Zool. Anstalt. Wien.,^ vol. i.) 



Through the cone-point consisting of ganglion-cells the 

 nerve-fibres come forth rectilineally, and cross each other 

 shortly after passing out as they keep their direction (12). 

 After crossing they extend themselves again over a larger 

 space, and at the same time the nerve-fibres always become 

 connected in groups so as to form bundles. Between these cord- 

 like bundles lie numerous nuclei of the most diff'erent form 

 and size, probably appertaining to the connective tissue. 



The exterior ganglion-opticum consists of a threefold layer 

 of small ganglion-cells (9), and a single stratum of long pali- 



^ In the embryonic state perfect cells, with much cell-body, form the bark 

 of the ganglion in insects ; the cell-substance diminishes more and more in 

 the course of the development, the deeper layers of the ganglion increasing 

 probably at its expense. 



