Herrick, Morphology of Brain of Bony Fishes. 51 



ten or twelve of these cells occupy the thickness of this sixth 

 layer ; toward the anterior part of the tectum this layer passes 

 continuously into the fornix 



"The other species of nervous elements in the tectum is 

 found in the second layer; these are long, fusiform, cell-like 

 swellings of the radial fibres, which are finer at the inner end 

 than at the outer ; it is somewhat difficult to measure their length 

 owing to the gradual transition between the fibre and the cells, 

 it may however be said to vary l)etween 0.018 and 0.040 millim.; 

 the width is more constant, being seldom more than 0.005 

 millim., luit occasionally reaching as much as o 007 millim.; the 

 nucleus measures about 0.005 by 0.003 millim. These cells are 

 not enclosed in a space, but the neuroglia is in apposition to 

 their external surface. The fibre which passes from the inner 

 end of these cells is the finer, and can be traced into the 

 smoothly striated third layer; the fibres from the sixth layer can 

 be traced into the same stratum from the other side, from which 

 circumstance the presumption arises that the small cells of the 

 external layer stand in connection with the fusiform bodies just 

 described. Stieda places these cells in his third or striated layer, 

 and considers them to belong to the neuroglia ' Grundsubstanz.' 

 This does uot seem to be cpiite correct; they are situated, in 

 fact,'in the layer which he terms 'die iiussere Langsfaserschicht.' 

 Their nervous character can scarcely be doubtful ; they resemble 

 in fundamental structure the cell-like swellings on the fibres of 

 the olfacory lobe, and also the Purkinje cells of the second 

 Layer of the cerebellum, as the latter would appear if drawn out 

 and stretched so as to be made long and thin. The outer pro- 

 cesses of these cells can be traced under favorable ciicumstances 

 into the outer finely granular layer of the tectum." 



With reference to this account, which is laboriously de- 

 tailed, it must be admitted that many of the discrepancies en- 

 countered are to be referred to the effects of the sudden bath in 

 absolute alcohol. 



The following is a condensed account of the tectum opticum 

 of Acipenser derived from Goronowitsch : 



The tectcum opticum of the sturgeon has a characteristically 

 laminated structure common to all vertebrates. Three layers are 

 distinguished beginning from the periphery. ^'^\\& outer layer has 



