PERRIN ET AL.: GROWTH AND REPRODUCTION OF SPOTTED PORPOISE 

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2 3 4 5 6 7 8 9 10 II 12 13 14 15 16 17 18 



CORPORA (number) 



FIGURE 24. — Relationship between body length and number of 

 corpora in Stenella attenuata. Average (bar), ± two standard 

 errors (box), range (vertical line), and sample size shown. 



Table 2. — Results of analyses of length and age at attainment 

 of sexual maturity in Stenella attenuata, with comments (in 

 parentheses) on pros and cons of the methods. Lengths and layer 

 counts predicted with the growth equations are in parentheses. 



luteum of pregnancy arises from the ruptured fol- 

 licle and has an important secretory function in 

 maintaining early pregnancy in all mammals 

 and full gestation in most (Amoroso and Finn 

 1962). The gross and microscopic structures of 

 corpora lutea in various delphinids, including S. 

 attenuata, have been described by Harrison et al. 

 (1972). 



The corpus luteum decreases in size during ges- 

 tation (Figure 26). Of 242 females with corpora 

 lutea, 229 were pregnant. Eleven with fetuses 

 less than 20 mm long (range 1 to 20 mm) had 



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140 150 160 170 ISO 190 



BODY LENGTH (cm] 



200 210 



Figure 25. — Relationship between body length and diameter 

 of the largest Graafian follicle in Stenella attenuata. Open dots 

 represent females with corpus luteum. For length ^160 and 

 n 5=10, means (circled symbols) and ranges shown. Forn 3=30, ± 

 two standard errors are shown. Not included are 27 "senile" 

 specimens with follicles <0, 1 nmi and five juveniles 88 to 122 cm 

 with 0- to 1-mm follicles. 



corpora with diameters of 23 to 29 mm (average 

 26.0 mm, SD 2.90). The mean diameter dropped 

 sharply to 23.6 mm (range 21 to 27 mm, SD 2.27) 

 in 17 females with fetuses between 20 and 100 

 mm (using Student's t, means are significantly 

 different at a = 0.01). This amounts to about a 

 32% decrease in luteal volume. Size of the corpus 

 luteum continues to decrease at a slower rate, to 

 22.2 mm (range 19 to 28 mm, SD 1.79) in females 

 with fetuses 700 to 825 mm (average length at 

 birth is 825 mm) long, a further decrease in vol- 

 ume of about 15%. Luteal volume in females with 

 near-term fetuses is only about half of that 

 shortly after conception. Mean diameter in 10 

 females with fetuses longer than average birth 

 length (825 mm) was 24.0 mm (range 20 to 26 mm, 

 SD 2.21, greater than mean for 700 to 825 mm at 

 a = 0.01), a volume difference of about 38% more 

 than for fetuses 700 to 825 mm long. Delayed re- 

 gression (or re-enlargement) of the corpus luteum 

 is apparently correlated with greater-than- 

 average length at birth. 



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