684 GREENE. [Vol. XV. 



developing organ (PI. XLf Figs. 21, 23, and 24). The matrix 

 of these connective-tissue cells is gradually converted into 

 the modified fibrils which characterize the adult reflector 

 (PI. XXXIXf Figs. 9-1 1, and PI. XU Fig. 24). These fibrils 

 are at first intermixed with a large amount of ordinary con- 

 nective-tissue strands but ultimately form almost the entire 

 mass. The pigment cells likewise increase in number and 

 form masses of cells about the reflector, especially in organs 

 on the side of the body. 



Organs in different rows do not appear at the same time. 

 Those on the mandible and ventral surface of the body appear 

 first, and since they reach the highest development are taken as 

 types. The lower series of the lateral line at 20 mm. is not 

 farther advanced than organs of the ventral line at 11 to 12 

 mm. Those organs above the lateral line appear later and are 

 always very rudimentary. In fact, such organs as I have des- 

 ignated rudimentary are never present above the lateral line 

 and on the dorsal surface of the body up to the time when the 

 embryos become free-swimming, a length of at least 25 mm. 



VII. Function of the Phosphorescent Organs. 



I have kept specimens of Porichthys in aquaria at the Hop- 

 kins Seaside Laboratory, and have made numerous observations 

 on them with an effort to secure ocular proof of the phospho- 

 rescence of the living active fish. The fish was observed in 

 the dark when quiet and when violently excited, but, with a 

 single exception, only negative results were obtained. Once 

 a phosphorescent glow of scarcely perceptible intensity was 

 observed when the fish was pressed against the side of the 

 aquarium. Then, this is a shore fish and quite common, and 

 one might suppose that so striking a phenomenon as it would 

 present if these organs were phosphorescent in a small degree 

 would be observed by ichthyologists in the field, or by fisher- 

 men, but diligent inquiry reveals no such evidence. 



Notwithstanding the fact that Porichthys has been observed 

 to voluntarily exhibit only the trace of phosphorescence men- 

 tioned above, still the organs which it possesses in such num- 



