PERRIN ET AL.: GROWTH AND REPRODUCTION OF SPOTTED PORPOISE 



Nine obviously postpartum females had cor- 

 pora lutea 13 to 25 mm in diameter (Figure 26). 

 Four lactating females with uteri not obviously 

 distended had corpora lutea in the same size 

 range. Average luteal volume in these lactating 

 animals was less than half of that in animals at 

 parturition. Some of these 13 cases may represent 

 miscarriages. 



The corpus luteum of pregnancy shrinks still 

 further during the suckling period, losing its 

 glandular appearance and becoming a corpus al- 

 bicans. Nine of 197 lactating females without cor- 

 pora lutea each had a single corpus albicans, 

 which must represent the regressed corpus 

 luteum of the first pregnancy. These corpora (Fig- 

 ure 26) were approximately spherical and 5.9 to 

 10.6 mm in diameter (average 8.5 mm). The lower 

 end of this range — about 6 mm — must approx- 

 imate the limit of regression during the suckling 

 period (about 11.2 mo; see below). The small 

 number of lactating females with corpora lutea 

 (13) compared to the number with only copora al- 

 bicantia (197) indicates that initial regression fol- 

 lowing parturition must be very rapid, perhaps 

 occurring in less than 15 days. Still further re- 

 gression in size and histological structure of the 

 corpus albicans of pregnancy probably occurs. 

 Many adult females have a large corpus albicans 

 (in most cases, one of several) between 3 and 6 

 mm in diameter (Figure 26) with greatly degen- 

 erated structure. Unless these corpora all repre- 

 sent ovarian events not resulting in pregnancy, 

 i.e., the females are all completely barren, the 

 corpus albicans of pregnancy must decrease in 

 diameter during a resting period following a 

 pregnancy, to possibly as little as 3 mm. 



Multiple corpora lutea are uncommon in S. at- 

 tenuata. They were encountered in only 2 out of 

 258 females with corpora lutea. One of these was 

 pregnant with twin fetuses (males, 83 and 86 

 mm) in the left horn of the uterus. The left ovary 

 contained two corpora lutea of approximately 

 equal size, each possessing a surface scar of ovu- 

 lation, together with seven corpora albicantia vis- 

 ible on the surface. The right ovary was devoid of 

 scars. Another female with two corpora lutea had 

 a 592-mm fetus (male) in the left horn of the 

 uterus. The left ovary looked very much like that 

 of the specimen with twin fetuses, having two 

 corpora lutea of approximately equal size and 

 eight corpora albicantia on the surface. Neither 

 corpus luteum bore a discernible surface scar. The 

 right ovary was unscarred. There are two possible 



explanations for the presence of two corpora lutea 

 in this specimen: 1) one of them was an accessory 

 corpus, or 2) one of a pair of twin fetuses was 

 aborted during early pregnancy. In any case, the 

 incidence of multiple corpora lutea is very low in 

 S. attenuata, less than 1% in the sample 

 examined. This is in sharp contrast to some other 

 cetaceans, in which rates of presence of accessory 

 corpora range to 15.6% iDelphinapterus leucas 

 — Brodie 1972). The contribution of double and 

 accessory corpora lutea to the accumulation of 

 corpora albicantia can be considered to be neg- 

 ligible in S. attenuata. 



Corpora albicantia in S. attenuata represent 

 both regressed corpora lutea of pregnancy and re- 

 gressed corpora of ovulations that do not result in 

 pregnancy. This conclusion is based on the ac- 

 cumulation rate of corpora albicantia and on the 

 estimate of the mean length of the calving inter- 

 val (see below). We were not, however, able to 

 differentiate between small regressed corpora 

 lutea and regressed corpora of ovulation. This 

 impasse, also encountered by workers dealing 

 with other cetaceans (Harrison et al. 1972) is 

 caused by the wide and largely discordant varia- 

 tion in size, shape, surface texture, and internal 

 structure and color of the corpora albicantia. If 

 one looks at enough corpora, it is possible to find 

 corpora with these characters in almost any com- 

 bination of expressions. 



Harrison et al. (1972) found no more than six 

 corpora albicantia in the ovaries of any Stenella 

 female. In the present sample, however, nearly 

 half (44%) of the females had more than six cor- 

 pora, including the corpus luteum. Fifty-five 

 females of 1,131 had 15 or more corpora; one had 

 28 (Figure 27). Three thousand five hundred and 

 two corpora from ovaries of 530 females were 

 scored to six categories. These categories are 

 somewhat arbitrary in view of the continuity of 

 regression and the wide variation discussed 

 above, but, nonetheless, they are useful in 

 analyzing the course of regression. The numbers 

 and proportion of total corpora complement rep- 

 resented by each of these categories varies with 

 the total number of corpora (Table 3, Figure 28). 

 The categories were defined as follows: 



Type 1. Surface raised, smooth or slightly 

 wrinkled. Looks externally like a small corpus 

 luteum. Cortex white or yellow, with obvious 

 remnants of vascularization. Center solid or 

 loosely constructed, consisting mainly of white 



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