FISHERY BULLETIN: VOL. 70, NO. 3 



Figure 11. — Developmental stage of Lampanyctodes hectoris (Giinther). — A, 9.2-mm larva, R.R.S. Discovery Sta- 

 tion 1374; B, 9.2-nun larva, dorsal view. 



most ventral jaw photophore (Bra) and extend- 

 ing posteriad to the tail. Above these ventral 

 rows on each side was a lateral row that extended 

 from the middle jaw photophore (Br^) posteriad 

 to the anus. A third row began with the upper 

 jaw photophore (Bri) and ended with the upper 

 opercular photophore. Fraser-Brunner pro- 

 posed that the photophore patterns of all extant 

 lanternfish species were derived by upward mi- 

 gration of certain photophores on the ventral 

 and lateral rows of the ancestral form. His chief 

 evidence for such upward migration was that, 

 in present-day myctophids, certain lateral photo- 

 phores, such as the posterior two SAO and the 

 POL, lie above gaps in the ventral series. These 

 gaps were presumably produced by the upward 

 migration of photophores to the lateral position 

 they now occupy. He found other indirect evi- 

 dence in the presence of small modified scales 

 which overlie certain of the lateral photophores 

 in some species. Since these scales were out of 

 the meristic lines of the larger scales, Fraser- 

 Brunner concluded that they were scales that 



had been "taken with" the photophores during 

 their upward migration. 



Fraser-Brunner's (1949) hypothesis has re- 

 mained unchallenged or at least tacitly accepted 

 by workers up to the present; however, we be- 

 lieve that it contains a number of deficiencies 

 which warrant an alternative theory for the evo- 

 lution of the photophore pattern in lanternfishes. 

 Firstly, we believe that the presence of certain 

 lateral photophores above gaps in the ventral 

 row is tenuous indirect evidence of migration, 

 since there are many examples of lateral photo- 

 phores lying directly above photophores in the 

 ventral series, and there are equally numerous 

 examples of gaps in the ventral series with no 

 overlying photophores whatsoever. Further, we 

 find the presence of small specialized scales over 

 certain of the lateral photophores to be incon- 

 clusive evidence of upward migration from the 

 ventral series, since some lateral photophores 

 are overlain by normal-sized scales that are 

 aligned with the other scales in their row. Also, 

 if a photophore had carried its scale with it dur- 



558 



