682 GREENE. [Vol. XV. 



well differentiated to be counted in skins. But the ventral and 

 branchiostegal rows are not accompanied by sense organs, and, 

 therefore, furnish a crucial test as to the origin of the organs. 

 In the serial sections of the embryo mentioned above, the basal 

 layer of cells of the epidermis of the ventral side of the body is 

 slightly thickened in the region occupied by the adult ventral 

 line (PI. XL? Fig. 13). The thickening is produced by a more 

 rapid increase in the number of the epidermal cells in the 

 particular area. 



In the gastric row of the same specimen there is a similar 

 multiplication of cells just above the accompanying sensory 

 Anlage (PI. XL? Fig. 14). In this case the multiplication 

 of cells shows a sort of center toward which the surrounding 

 nuclei perceptibly converge. This is the beginning of a cell 

 aggregation which soon proliferates into well-marked centers or 

 groups, the antecedents of the individual organs of the line. 

 In this incipient stage of the gastric organs the cells lie imme- 

 diately against the cells of the sensory Anlage of the gastro- 

 gular row of sense organs, but they show no other evidence of 

 origin from it. In skins it happened in one instance that the 

 sensory Anlage of this row was torn free of the epidermis, and 

 the cells along its upper border were apparently undisturbed. 

 They were slightly increased in number, however, indicating a 

 stage comparable to that from the ventral line figured in cross- 

 section in PI. XL? Fig. 13, or in the corresponding line in 

 PI. XL? Fig. 14. 



Although it would seem impossible to affirm that the origin 

 of the phosphorescent organs in the gastric row is independent 

 of the sensory Anlage which has arisen by migration of cells, 

 yet I am convinced that such is the case. The above facts, 

 especially the independence of the origin of the rows above 

 mentioned not associated with sense organs, form the basis 

 of my belief that the phosphorescent organs arise by local pro- 

 liferation of cells from the epidertnis in the region which they 

 pertnancntly occupy. 



The further progress in the development of the phosphores- 

 cent organ consists in the rapid multiplication of cells, giving 

 rise to a distinct nodule which projects as a small papilla from 



