BENIRSCHKE ET AL.: OVULATION IN DOLPHINS 



specimens the findings are consistent with abor- 

 tion, two had marked endometritis. These latter 

 findings are summarized in Table 10. 



Table lO. — Group VI: Summary of experimental, nonpregnant 

 animals; 38 Stenella longirostris, 20 S. attenuata. 



S longirostris: 



19 (50°o) Fresh corpus luteum 



1 1 (29%) Well-established corpus luteum 



8 (21%) Degenerating corpus luteum — wrong gross diagnosis (2 en- 



dometritis; 2 unimplanted abortion?) 

 S. attenuata: 



9 (45%) Fresh corpus luteum 



3 (15%) Well-established corpus luteum 

 1 ( 5%) Misclasslfied. recently delivered 



7 (35%) Degenerating corpus luteum — wrong gross diagnosis ( 1 recent 

 abortion?) 



The findings of Perrin et al. (1976, 1977) indi- 

 cate that over 90^7^ of female genital tracts of S. 

 longirostris and S. attenuata contain a corpus 

 luteum because of their pregnancy. The possibility 

 that abortions of implanted pregnancies occur fre- 

 quently can be ruled out from the histologic ap- 

 pearance of the endometria in the majority of the 

 specimens from the experimental group. Early 

 embryonic death remains a possibility although 

 no evidence can be adduced for this. The present 

 study provides strong evidence that spontaneous 

 ovulation may occur in these species, at least that 

 the presence of a corpus luteum is not indicative of 

 pregnancy. Moreover, recent and as yet unpub- 

 lished results from our laboratory I J. Sawyer) 

 have identified hormonally the occurrence of 

 spontaneous ovulation in a Delphinus delphis 

 female that was kept in isolation. Evidence for 

 regression of corpora lutea in nonfertile cycles was 

 also found in our experimental group. It is possible 

 then that either ovulation is induced in a majority 

 of cycles or that a majority of dolphins become 

 pregnant when ovulating. In either case, it is not 

 likely that a count of corpora albicantia in dolphin 

 ovaries accurately reflects the number of past preg- 

 nancies. We were unable to differentiate with 

 certainty between the histologic appearance of a 

 corpus luteum of early pregnancy and one from 

 nonpregnant animals and cannot accept the al- 

 leged feasibility of the diagnosis of pregnancy 

 from the histology of only a corpus luteum. The 

 endometrial histology is a better guide. Whereas 

 accessory corpora lutea have been found in other 

 odontocetes ( Brodie 1 972 ), no such structures were 

 encountered in the genital tracts of these two 

 Stenella species. 



It would be useful to know from aquaria with 

 accurate historical information and pathologic 

 study at death whether older females that have 

 been kept in isolation since youth possess corpora 

 albicantia. Inasmuch as the question of artificial 

 insemination of exhibited animals has been raised 

 in the past (Hill and Gilmartin 1977) it can be 

 concluded that it would appear feasible without 

 the need of superovulation. 



From a practical standpoint it is suggested that 

 the following points be considered in future 

 studies. First, it would have been helpful to have 

 had a histologic sample of mammary gland and 

 vagina in all specimens to enhance histologic cor- 

 relations. Moreover, inasmuch as the hormonal 

 cycle of D. delphis is now being defined by modern 

 endocrine techniques undertaken by sequential 

 sampling of captive specimens it may be useful for 

 future studies to save, for endocrine analysis, an 

 aliquot of frozen serum. Potentially, such a study 

 would clarify the status of equivocal corpora lutea. 

 At the same time storage of fetal serum would 

 allow insight into the fetal endocrine behavior 

 which is known to differ so markedly between 

 species. Perhaps such comparative studies will ul- 

 timately give additional insight into the 

 phylogenetic descendency of Cetacea. 



This study extends the sparse literature that 

 exists on the morphology of the female reproduc- 

 tive organs. In general, the endometrial cycle is 

 similar to that illustrated schematically for sev- 

 eral whales (Slijper 1966) and for Globiocephala 

 melaena (Harrison 1949). In this latter species 

 Harrison (1949) also described the small superfi- 

 cial anastomosing vessels beneath the uterine 

 epithelium and, in three recently ovulated speci- 

 mens, he was unable to identify products of con- 

 ception. In a later contribution, Harrison et al. 

 (1969) suggested that while ovulation in Tursiops 

 truncatus appears to be of a reflex nature, that of 

 S. graffmani and Lagenorhynchus obliquidens 

 may be spontaneous as in G. melaena. Our own 

 findings cited above suggest, however, that in D. 

 delphis spontaneous ovulation occurs and one 

 wonders whether this then may not be the rule in 

 Cetacea. A resolution can come only from lon- 

 gitudinal endocrine studies of isolated females 

 from different species. Finally, as was the case in 

 most other studies of the morphology of Cetacean 

 reproductive organs, we observed no significant 

 pathologic features in these specimens other than 

 the endometritis described and occasional 

 parametrial parasitic granulomata. ^ 



527 



