FISHERY BULLETIN: VOL. 70, NO. 3 



13) more closely resembles the Hawaiian spinner 

 than does the adult, in that the margin of the 

 ventral white field is relatively smooth. The pat- 

 tern of the fetus of the eastern spinner (Figure 

 25) is also very close to the Hawaiian pattern, 

 with the tripartite effect of cape, lateral field, 

 and high ventral field being very pronounced. 

 The question of which sort of developmental 

 cline is involved, paedogenesis to the west or 

 gerontogenesis to the east, is however yet an open 

 one and must be settled by consideration of ad- 

 ditional lines of morphological and zoogeograph- 

 ic evidence. 



Pattern component analysis. — Comparison of 

 the color pattern of a partially albinistic 

 subadult whitebelly spinner (Figure 14) with 

 that of a normally pigmented individual of 

 the same sex and nearly the same length (Fig- 

 ure 13) affords insight into the mechanisms of 

 pattern formation. In the lighter-than-normal 

 animal, the cape, eye patch and stripe, gape 

 mark, dorsal fin, and flukes are as in the normal 

 specimen. The lateral field, flipper band, and 

 oblique genital mark are obscure, and the flippers 

 are white on both surfaces. White brushings 

 sweep up from the edge of the cape at about 

 midlength toward the dorsal fin. From these 

 facts, the inference can be made that the full 

 normal pattern is the result of the combined ef- 

 fect of two independent pigmentation systems, 

 one involving the cape and accessory stripes, eye 

 and gape marks, dorsal fin, and flukes, and the 

 other involving lateral field, flipper band, and 

 flippers. While the genital mark is not apparent 

 in the albinistic animal, the developmental pat- 

 tern of obliteration through development of the 

 lateral field suggests that it belongs to the cape 

 system. The difference among the Hawaiian, 

 whitebelly, and eastern spinners can be inter- 

 preted schematically in terms of these hypothet- 

 ical systems (Figure 26) , allowing a clearer pic- 

 ture to emerge of the possible patterns of geo- 

 graphical variation involved. Since the lateral 

 field appears in this sense to be the lateral por- 

 tion of a more extensive dorsal field overlaying 

 the cape, it is referred to below as an aspect of 

 a "dorsal field overlay." 



Among these three forms, the "dorsal field 



Figure 13. — Lateral (a), dorsal (b) , 

 and ventral (c) views of subadult 

 whitebelly spinner. Male, 164 cm, from 

 9°47'N, 133°25'W, August 11, 1970. 

 Perrin field no. WFP65 ; U.S. National 

 Museum 396017 (complete skeleton). 

 Rostrum damaged. Photographed aft- 

 er frozen for several months and 

 thawed in water. 



Figure 14. — Lateral (a) and dorsal 

 (b) views of albinistic subadult white- 

 belly spinner. Male, 154 cm, from 

 10°19'N, 135°38'W, August 5, 1970. 

 Perrin field no. WFP67; U.S. National 

 Museum 396020 (complete skeleton). 

 Compare with normally pigmented ani- 

 mal in Figure 13. Note dark flukes and 

 light flippers. Photographed after 

 frozen for several months and thawed 

 in water. 



overlay" is darkest and most extensive in the 

 easternmost form, and least so in the Hawaiian 

 form. It is not yet known whether the three 

 forms represent modes in a geographically con- 

 tinuously varying single species or two or more 

 reproductively isolated allopatric or sympatric 

 populations. 



OTHER DELPHINIDS 



The color patterns of other closely related del- 

 phinids can be similarly dissected into hypothet- 

 ical component systems. The patterns of three 

 forms of which I have directly examined live or 

 freshly captured dead specimens are analyzed in 

 Figure 27, with an attempt to define possible ho- 

 mologies for the component systems among the 

 species. As the first step in breaking down the 

 patterns into supposedly homologous compo- 

 nents, I attempted to define for each a cape with 

 associated markings, similar to that in the al- 

 binistic spinner described above. 



In the eastern Pacific spotted porpoise, Stenel- 

 la graffmani, (Figure 27, top) the general cape 

 system is very close to that of the spinners, with 

 the cape extending farther ventrad. The dorsal 

 overlay is less extensive than in any of the spin- 

 ners, and the flipper band runs forward to the 

 gape rather than to the eye. The area of con- 

 tact between the flipper band and the gape mark 

 in this and in similar spotted porpoise from other 



992 



