42: 



MALL. 



[Vol. VIII. 



apposition, so that the same principle applies to them as to the 

 nerve-cells, or to cells in general. 



Fig. 5 is a stage two clays in advance of Fig. 4. The fat 

 globules in this case show how the peripheral end of the cell is 

 breaking up into its prolongations. The process is beginning 

 to effect the basal end of the cells also. Practically all the 

 cells of the retina in this stage contribute to the formation of 

 the net-work of interlocking cells, and as yet no true nerve- 

 cells are present. In a stage later, Fig. 6, the lens is 



Fig. 7. — Section through the eye of Amblystoma (8 mm. long) nine days before 

 hatching. X 133 times. S, spongioblast ; N, neuroblast. 



separated from the ectoderm, and the secondary optic vesicle 

 is more cup-shaped. The net-work of fibrils is still outlined 

 by the pigment granules and they form such an intimate 

 meshwork that it is impossible to separate the cells. There 

 seems to be a complete union of protoplasm of the cells, but 

 on account of the mode of development as well as on account 

 of histological principles I consider this only apparent, and not 

 real. Already in this stage some of the nuclei are beginning 

 to move towards the free border of the retina, and this is 

 greatly increased a day or two later (Fig. 7). 



