EARLY DEVELOPMENT OF THE TEN-POUNDER 



631 



right. I found the counts for the two sides to 

 differ by as many as 3, with a range of 27-33 for 

 one side for juveniles and adult. Berg (1947) 

 gave the range for Elops as 27-35, and Regan 

 (1909) gave 28-36. 



GULAR PLATE 



The gular plate (a long, flat, narrow bone be- 

 tween the rami of the mandibles), which distin- 

 guishes the tarpon and ten-pounder from the bone- 

 fish, develops during the mid-metamorphic period. 



Table 8. — Variation in number of gill rakers on upper and 

 Imeer limbs of first arch of mid-metamorphic larvae to 

 adults 



Table 9.- 



-Yariation in number of gill rakers on first arch 

 of mid-metamorphic lart^ae to adults 



SCALES AND LATERAL LINE 



Cycloid scales and the lateral line are first pres- 

 ent at about 50 mm. in the late metamorphic 

 period. The lateral line and scales extend onto 

 the caudal fin, and the number of scales along the 

 lateral line ranges 105-115. The head is unsealed 

 in Elops. Hildebrand (1943) gave the range of 

 scales as 103-120, with scales appearing at about 

 50 mm., and scalation complete by about 60-65 

 mm. Sheaths of scales at the bases of the dorsal 

 and anal fins are developed by about 60 mm. 

 Several long, and irregularly shaped axillary 

 scales at the insertions of the pectoral and pelvic 

 fins are present at about 50 mm. 



499662 0—59 3 



ADIPOSE EYELID 



The adipose eyelid is present by about 50 mm. 

 in the late metamorphic period, covering very 

 little of the anterior and posterior margins of the 

 eye (fig. 15) . During the juvenile period the eye- 

 lid extends farther over the eye, and on the adult 

 (380 mm.) all of the eye is covered except a 

 vertical slit the width of the pupil (fig. 17). 



CHANGES IN BODY FORM 



The body of the leptocephalus at 5.3 mm. (fig. 

 2) is ribbonlike; long, thin, and deep (deepest 

 about midway between the head and the anus), 

 and tapers gently to a rodlike urostyle (or tip of 

 notochord). The head is broader and slightly 

 deeper than the body. By about 10 mm. (fig. 3) 

 the body is deeper than the head, and the head is 

 triangular in dorsal aspect. By about 20 mm. the 

 caudal fin is forked, and the body is still ribbon- 

 like in appearance. At the end of the leptoceph- 

 alus period (fig. 7) the head is relatively smaller 

 than at any other size or stage of development ; the 

 body is long, thin, and deep ; and fins are not yet 

 prominent. During the early metamorphic pe- 

 riod the body shortens and thickens slightly while 

 the head remains a constant length. During the 

 mid-metamorphic period the ribbonlike appear- 

 ance is lost as the body thickens, and the head loses 

 its triangular shape. Also during the mid-meta- 

 morphic period the anal and dorsal fins shift 

 anteriorly (this change in position is discussed 

 under "Regressions of body parts on standard 

 length"). By the end of the late metamorphic 

 period the body form is generally that of the 

 adult; long, round, and tapered at the head and 

 caudal, with the fins large and well developed 

 (fig. 15). 



PIGMENTATION 



The 5.3-mm. leptocephalus (fig. 2) is translucent 

 except for a silver eye with a black pupil and a few 

 melanophores scattered along the dorsal aspect of 

 the digestive tract. During the leptocephalus 

 period the melanophores along the digestive tract 

 increase, and some develop between the body myo- 

 meres, along the mid-lateral line of the body, on 

 the caudal fin, and between the myomeres at the 

 anal ray bases (figs. 2 to 7). The largest lepto- 



