FISHERY BULLETIN: VOL. 74, NO. 2 



albicantia. They also typically had very small 

 Graafian follicles (Figure 31). A consideration of 

 these females bears on the question of persistence 

 of corpora albicantia. Sergeant (1962) encoun- 

 tered similar females in Globicephala. They com- 

 prised about 5% of adult females. He called them 

 "senile" and concluded that the ovarian scars in 

 these animals represent some residual subset of 

 the maximum complement of corpora of preg- 

 nancy, ovulation, and other events. He implied 

 that they probably are the corpora of pregnancy, 

 since those corpora are larger at the outset and 

 presumably less likely to regress to the point of 

 macroscopic disappearance. The ovarian data for 

 S. attenuata do not support this hypothesis of dis- 

 appearance of some corpora in regressed ovaries. 

 The regressed ovaries have 10 to 15 corpora (Fig- 

 ures 30 and 31). The ovaries of other, still repro- 

 ductive females are larger and have 16 to 27 cor- 

 pora, although follicles are typically smaller than 

 in reproductive females w^ith fewer corpora (Fig- 

 ure 31). Three alternative hypotheses explain 

 this apparent dichotomy in females with 10 or 

 more corpora: 



1. The usual maximum number of corpora is 

 about 21, and some corpora disappear in 

 postreproductive females, i.e., the "senile" 

 group in Figure 30 properly belongs at the 

 far right side of the plot at the end of a 

 downward trend in ovary weight (the hy- 

 pothesis of Sergeant 1962). 



2. Corpora are laid down at about the same 

 rate in all individuals, but some become 

 postreproductive at about 10 to 15 corpora 

 while others continue to accumulate corpora 

 (16 to 27) until a greater age, i.e., the corpo- 

 ra scale in Figure 30 is effectively an age 

 scale. Under this hjrpothesis, corpora do not 

 disappear. 



3. Corpora are accumulated at rates varying 

 widely among individuals, but the typical 

 maximum complement is 10 to 15 corpora, 

 i.e., the reproductive females with more 

 than 15 corpora in Figure 30 properly belong 

 in the body of the distribution in the left 

 two-thirds of the plot. A possible explana- 

 tion for widely varying rates of accumula- 

 tion is that some females are more fecund 

 and the senile period is reached with some 

 maximum number of pregnancies, so that 

 the varying ratios of corpora of pregnancy to 

 corpora of ovulation may produce the appar- 



ent dichotomy. Sergeant (1973) found 

 greatly varying individual rates of ovulation 

 in the white whale, Delphinapterus leucas. 



In order to examine these alternative hypoth- 

 eses, the females in Figure 30 and 31 with 10 or 

 more corpora were examined in three groups — 

 A, B, and C: 



A. 10 to 15 corpora, reproductively active 



(corpus luteum and/or Types 1 and 2 

 corpora albicantia). 



B. 16 or more corpora, reproductively active. 



C. 10 to 15 corpora, postreproductive (ovaries 



regressed, no corpus luteum or Types 

 1 or 2 corpora albicantia). 



The three groups were compared in terms of 

 corpora count, weight of ovaries, size of largest 

 follicle, number of dentinal layers, total length, 

 and relative corpora counts in left and right 

 ovaries (Table 5). Only nonpregnant females were 

 included in the sample for ovary weight. Follicle 

 size was examined separately for pregnant and 

 nonpregnant animals. 



Ovary weight and follicle size for nonpregnant 

 animals decline progressively from A to C. This is 



Table 5. — Characteristics of females of Stenella attenuata in 

 groups A, B, and C (see text). 



258 



