WILLIAMS: MIGRATION OF EYE IN PSEUDOPLEURONECTES. 41 



Passina: from without inward, the tectal layers are as follows : 



(1) A thiu outer layer, composed principally of nerve fibrillations 

 with a few nerve cells. In this layer the ependymal fibrillations end. 

 A corresponding layer is recognized by writers on the finer anatomy of 

 the tectum in the bony fishes, from Stieda ('67) onwards, except by 

 Fusari ('87, '96) and Van Gehuchten ('95). Eusari ('87) described a 

 layer of vascular connective tissue beneath the pia, and later ('96) his 

 first layer of the tectum was made to embrace this vascular layer and 

 the optic-fibre layer. 



(2) The layer of the medullated optic fibres. This is the continua- 

 tion of the optic tract and is recognized as a separate layer by all writers 

 on the tectum. ' 



(3) A layer of optic fibrillations. This is not made a distinct layer 

 by Stieda ("67), but Mayser ('81) and nearly all writers since his time 

 have emphasized its presence. 



(4) A spindle-cell layer. 



(5) The fillet layer,' composed of longitudinal fibres and cross com- 

 missural fibres. Stieda considered the fibres, which here run in two 

 directions, as two layers. C. L. Herrick ('91-92) describes a layer of 

 commissural fibres beneath the fillet connecting the two optic lobes. 



(6) The " gray " layer. 



(7) The reticulate and ependymal layer. Some authors consider 

 that this is composed of two distinct layers. The reticulate portion 

 is not described at all by Neumayer ('95), Van Gehuchteu ('95) nor 

 Edinger ('96). 



Mirto ('96) based his division of the tectum into layers on the shapes 

 of the cells which he was able to demonstrate by the Golgi method. 

 Following Cajal's work on the tectum of birds, he describes fourteen 

 layers. 



The degeneration methods did not yield much of importance in my 

 hands, although the flounder, owing to its habit of protruding the eyes, 

 is a favorable fish on which to operate. The animals, even the very 

 small metamoi'phosed fishes, stand the shock of the removal of the eye 

 well and bleed very little from the operation. The specimens tried by 

 the Marchi method were very brittle, and demonstrated but one point 

 clearly, that the sixth (nerve-cell) layer was reduced. Fusari ('96), who 

 used the "Weigert-Pal staining method on a Cyprinoid, concluded that 

 all the tractus fibres degenerated when the eye was removed. Krause 

 ■ ('98), after the Marchi treatment of fish from which the eyes had been 

 removed, found that about one-tenth of the tract — mostly distributed 



