tion of the population. In Delphinus delphis. an 

 individual's proximity to sexual maturity can be 

 accurately assessed using appropriate mor- 

 phometric data. 



Materials and Methods 



I used 35 male and 52 female Delphinus delphis 

 specimens collected in southern California waters 

 from 1971 to 1974. 



The body weight in kilograms, body length in a 

 straight line to the nearest centimeter from tip of 

 the snout to the anterior portion of the fluke notch, 

 dentine layers, bone development in the flippers, 

 testes weights, and the numbers of scars on the 

 ovaries were recorded. 



Teeth were usually from the posterior one-third 

 of the left mandibles; otherwise the largest teeth 

 available were used. A longitudinal section 0.368 

 mm thick was cut from the center of each tooth, 

 and samples were cleaned in a weak solution of 

 ammonia. After rinsing with water, the sections 

 were etched in \-2'^i^ formic acid at room tempera- 

 ture until the dentine growth layers were distinct, 

 usually 6-12 h. Sections were mounted on micro- 



scope slides in an ethanol solution and examined 

 with transmitted light. 



One light and one dark band were considered as 

 one dentine layer. The interval for dentine lami- 

 nar deposition is unknown for the D. delphis in the 

 present study but I assume that the bands were 

 laid down at regular intervals. Delphinus delphis 

 ponticus Barabash of the Black Sea are reported to 

 have two sets of alternating layers each year 

 (Kleinenberg and Klevezal 1962). 



Because different bones fuse at different times 

 in the spotted, Stenella attenuata, and the spinner 

 S. longirostris, porpoises (Perrin 1972), I used the 

 development of the epiphyses and their fusion to 

 the diaphyses of the flipper bones as the indicator 

 for physical maturity of the specimens. Each flip- 

 per was assigned an index by scoring the degree of 

 epiphyseal fusion visible in radiographs: when 

 no epiphysis had been formed; 1 when the 

 epiphysis had been formed but had not started its 

 fusion to the diaphysis; 2 when the epiphysis and 

 diaphysis were in the process of fusing; and 3 when 

 the epiphysis and diaphysis were fused. The distal 

 ends of the radius, ulna, metacarpals, and pha- 

 langes of each fiipper were scored (Figure 1). The 



Figure l.— Process of fusion of the 

 epiphyses to the diaphyses in the flipper 

 of Delphinus delphis. The flipper 

 labeled A has a score (see text) of 18; B, 

 49; and C. 72. 



296 



