46 Journal of Comparative Neuroi.ogy. 



roglia stroma, nerve cells and fibres develop. The cells develop 

 from the neuroblasts of the ventricular region and accumulate 

 between the connective cells up to the level of the first fibre belt, 

 forming a basal cellular zone. The upper portion becomes func- 

 tional and some cells migrate towards the periphery. By the 

 gradual thickening of the tectum, the ganglionic layer is sepa- 

 rated from the ventricular surface by an interval, 1, Fig. i, Plate 

 VII. The relation between the connective and nerve cells is 

 well shown in Fig. 2, of the same plate. It seems to me that 

 only the outer portion of the dense zone of nerve cells is func- 

 tional and it is only with these that a fibrous connection has been 

 observed. Fig. 3, Plate IX. The first layer of the tectum, be- 

 ginning from tbe ventricle, therefore, consists of columnar 

 epithelium cells whose protoplasm in the adult is more or less 

 shrunken and whose nucleus may still remain distinct or may 

 become imbedded in a thin layer of protoplasm adjoining the 

 walls. The walls may collapse beneath the ganglion layer and 

 there is frequently an intricate folding which produces a peculiar 

 appearance in section, but Fusari has completely misinterpreted 

 this appearance in Plate III of his work.' The appearance of 

 a brush-like radiation of fine processes is illusory and in perfectly 

 prepared specimens, not too much dragged in cutting, the walls 

 of the cylindrical epithelium cells can still be followed. Above 

 this level the whole tectum becomes charged with a dense mass 

 of glatinous matter, giving it a homogeneous appearance. The 

 (generally collapsed) walls of the connective cells pass directly 

 toward the periphery and in some cases enclose nuclei with sur- 

 rounding protoplasm. Whether these nuclei have sim]jly re- 

 treated from the ventricular surface, or whether a single epithe- 

 lium cell may have more than one nucleus, is uncertain, but at 

 the peripheral terminus there is always a small fusiform cell-like 

 body, as indicated in Figs, i, 2, Plate IX. These were appar- 

 ently figured by Fusari, as terminal expansions of ganglion-cell 

 fibres in the plate above referred to. 



It is only in well-preserved material that the distinction be- 

 tween the nuclei of the ventricular 'epithelium and the internal 



lAtti de Lincei Mem. cl. .sc. fis. ecc Ser. 4, Vol. IV. Intoriia all; 

 fina anatomia dell' Encefalo dei Teleostei. 



