EARLY DEVELOPMENT OF THE TEN-POUNDER 



621 



Taft for comments and suggestions on statistical 

 treatment of the data, 



METHODS AND DATA 



All measurements less than 50 mm. were made 

 to the nearest 0.1 mm. with a micrometer eyepiece 

 and binocular stereoscopic microscope (eye diam- 

 eters less than 2.0 mm. were recorded to the second 

 decimal) ; and those exceeding 50 mm. were made 

 to the nearest half or whole millimeter with draft- 

 ing dividers and a Paragon scale. Scale draw- 

 ings of specimens 34.2 mm. and smaller were made 

 with the aid of a calibrated grid reticule, and those, 

 of the 67.4-mm. and larger specimens were made 

 from tracings of enlargements of photographic 

 negatives. 



Original measurements were used in the graphs, 

 figures 25 to 30. The regressions of body parts on 

 standard length were determined by the method 

 of least squares. Unless otherwise stated, speci- 

 men lengths are standard length measurements. 

 Hollister (1936) and Evans (1948) procedures 

 were followed in staining specimens with alizarine 

 red to show ossification. 



Method of making plankton tows was that of 

 Anderson, Gehringer, and Cohen (1956). Bi- 

 weekly sampling with a seine in beach and marsh 

 habitats was done at the same place, at approxi- 

 mately the same tide conditions, low tide on the 

 beach and high tide in the marsh. 



DEFINITIONS OF TERMS 



Total length. Distance from tip of snout to most pos- 

 terior projection of caudal fin. 



Standard length. Distance from tip of snout to tip of 

 urostyle (or notochord) or posterior border of hypural 

 bones. 



Head length. Distance from tip of snout to posterior 

 fleshy margin of opercle. 



Head depth. Vertical measure of head at angle of jaws. 



Head width. Horizontal distance between verticals at 

 lateral margins of eyes. 



Eye diameter. Horizontal distance, width. 



Body depth at pectoral. Measure of depth at insertion 

 of pectoral fin. 



Snout to dorsal. Distance from tip of snout to origin 

 of dorsal tin. 



Snout to pelvic Distance from tip of snout to inser- 

 tion of pelvic fin. 



Snout to anal. Distance from tip of snout to origin of 

 anal fin. 

 Meristic Counts : 



Dorsal, anal, pelvic, and pectoral fin rays. Total num- 

 ber of rays, including rudiments. 



Caudal fin rays. Listed as : dorsal secondary -(-prin- 

 cipal -f ventral secondary rays (including rudiments). 

 The full complement, 10 dorsal and 9 ventral principal 

 rays, with 8-9 dorsal and 6-8 ventral secondary rays. 

 Principal rays are attached to the hypurals and include 

 all branched rays plus one upper and one lower unbranched 

 ray (one or more small secondary rays are also attached 

 to the anteriormost hypural). In small specimens some 

 of the principal rays which eventually branch were not 

 branched. 



Teeth. Number in each side of the upper and lower 

 jaws. 



Myomeres. Number of body myomeres (last few in 

 caudal region are indistinct) . 



Gill rakers. Total number, including rudiments, on 

 upper and lower limbs of first gill arch, on one side. 



Number of the myomere at dorsal, pelvic, or anal fin 

 origin, «!€. The number of the myomere whose dorsal or 

 ventral extremity approximates the position of part 

 involved. 



Number of scales. Lateral line scales, counted from 

 opercular flap to posterior scale on caudal fin. 



There are two periods during the larval develop- 

 ment of the ten-pounder in which the length of 

 the larva increases, and one in which the length 

 decreases. First is the "leptocephalus" period of 

 initial length increase to the size at which shrink- 

 ing commences (my smallest leptocephalus is 5.1 

 mm. standard length and the largest is 43.3 mm.). 

 The second period is "early metamorphic," and 

 includes those individuals shrinking in length 

 down to about 25 mm., the size at which marked 

 changes in form begin. Because it was not always 

 possible to distinguish those in the final stages of 

 shrinking from those undergoing initial increase 

 following shrinking, these individuals were com- 

 bined in the period, "mid-metamorphic." In- 

 cluded are individuals undergoing the final few 

 millimeters of length decrease, and the first few 

 millimeters of subsequent length increase, or 25 

 mm. down to about 18-20 mm. and up to 25 mm. 

 (characterized by loss of ribbonlike form, shifting 

 of fins, and development in fins) . 



At about 25 mm., after length begins to increase 

 again, the fish is still larval (without full com- 

 plements of fin rays, branchiostegals, and gill 

 rakers; scales; lateral line, etc.). From 25 mm. 

 to about 60 mm., these characters are forming, 

 and the period is called "late metamorphic." At 

 about 60 mm. the fish is a miniature adult, and is 

 called "juvenile." 



