FISHERY BULLETIN: VOL. 70, NO. 3 



Suprocaudol gland 

 Infrocaudal gland 



j AO posterior(AOp) 

 5 



AO anterior (AOo) 



Figure 4.— Diagram of characteristic photophore groups of adult myctophids (modified 

 from Nafpaktitis and Nafpaktitis, 1969 and Fraser-Brunner, 1949). 



larger specimens in the series. The next to de- 

 velop are the Vn; they appear anteroventral to 

 the eye in the 11.3-mm larvae and become pro- 

 gressively cup-shaped as development proceeds. 

 At the end of the larval period they are the 

 largest photophores present. During transfor- 

 mation they begin to be overlain with tissue and 

 bone so that they are difficult to see in juveniles 

 and adults; this is doubtless why they have been 

 overlooked by recent authors (Fraser-Brunner, 

 1949; Nafpaktitis and Nafpaktitis, 1969). The 

 fourth pair of photophores to develop are the 

 VLO; they first appear slightly posterior to, but 

 well above, the bases of the pelvic fins in a 13,4- 

 mm larva. 



The four pairs of photophores described above 

 are the only ones to develop until the larvae reach 

 about 15-mm length. In a series of five larvae 

 14.9-15.7 mm long, a number of other photo- 

 phores are beginning to appear. In the jaw re- 

 gion one is visible just below the terminus of 

 each maxillary, and another is forming above 

 and slightly anterior to the end of the maxillary. 

 One or two others are developing in a line ex- 

 tending dorso-anteriad from the latter cheek or- 

 gan. Dorsally on the head, a photophore is deve- 

 veloping above the lateral margin of each olfact- 

 ory lobe. In the PO series two pairs are evident, 

 one slightly posterior to the juncture of the 

 cleithra and another pair equidistant between 



this pair and the most posterior pair, described 

 above, A VO pair is developing midway between 

 the bases of the pelvic fins and the anus. Farther 

 posterior on the body, the SAO3 are developing as 

 are the posteriormost Pre pair. 



The photophore pattern is augmented further 

 in the three remarkable transforming specimens 

 illustrated in Figures 2 and 3, in which the adult 

 pattern of photophores is clearly emerging. The 

 three represent a developmental series of which 

 the 17.6-mm specimen is the least advanced, fol- 

 lowed by the progressively more advanced 16.7- 

 and 17.5-mm specimens. In the 17.6-mm speci- 

 men the previously described photophore pattern 

 on the head is augmented by several organs be- 

 low and to the rear of the eye, by a line of organs 

 along the lower jaw, and by several on the oper- 

 cle. On the body a PLO and one PVO is present 

 at the pectoral fin base, several organs are form- 

 ing above the vent, and two POL are arranged 

 horizontally above the end of the anal fin. In 

 addition, two horizontal lines of photophores are 

 beginning to appear, one above and one below the 

 lateral line. The adult photophore arrangement 

 of Scopelopsis is clearly manifest in the 16.7- 

 and 17.5-mm specimens. Photophores are be- 

 ginning to cover the head in a definite pattern; 

 some of these are considerably larger and more 

 defined than others. On the body the many reg- 

 ular rows of secondary organs are emerging, al- 



548 



