FISHERY BULLETIN: VOL. 78, NO. 2 



Table 9.— Group Vic: Experimental group with degenerating corpora lutea. Specimen no. 1-8 Stenella longirostris; no. 9-15 S. 



attenuata. 



dometritis. Two others had marked endometrial 

 stromal edema in addition to having horns of dif- 

 ferent lengths. The possibility of abortion exists in 

 these animals but this cannot be proven. Finally, 

 one animal of this heterogeneous group (no. 12, 

 Table 9) had equal uterine horns ( 18 cm) and pos- 

 sessed corpora albicantia in addition to a de- 

 generating right-sided corpus luteum. The 

 endometrium with hyalinization and capillary 

 development suggested recent pregnancy but be- 

 cause of the size of the uterus (205 g) it appears 

 likely that a recent right-sided pregnancy had 

 ended in abortion. 



DISCUSSION 



Although conclusive proof is lacking, the results 

 support the notion that dolphins may ovulate 

 spontaneously, at least at times. Control material 

 of different reproductive phases (96 specimens) of 

 the two species of dolphin investigated, the east- 

 ern spinner dolphin, S. longirostris , and the spot- 

 ted dolphin, S. attenuata, provided a life history of 

 the macroscopic and microscopic events in the 

 uteri and ovaries of these species for the first time. 

 The principal findings were the following: In three 

 immature animals neither corpora lutea nor cor- 

 pora albicantia were present in the ovaries but 

 Graafian follicles were forming. The endometrium 

 had tubular glands. Six mature animals without 

 corpus luteum all were found to have one or more 

 corpus albicans, the horns were disparate in size, 

 five had stretch marks as an excellent sign of 

 former pregnancy, in most the inactive endome- 

 trium possessed inflammatory cells, hyalinization, 



had hemosiderin macrophages as indications of 

 former pregnancy. Eleven of twelve early preg- 

 nant animals with embryonic sizes of 1-53 mm 

 had the pregnancy in the left horn; one in the right 

 on which side the corpus luteum was also located. 

 The endometrium of the earliest pregnancy had 

 characteristic changes that should allow preg- 

 nancy diagnosis even if the embryo is overlooked 

 or lost. Six late pregnant specimens had their cor- 

 pus luteum in the left ovary, typical epitheliocho- 

 rial implantation and again characteristic en- 

 dometrial histology. Eleven lactating females 

 were studied, none of which had a corpus luteum, 

 but all possessed at least one corpus albicans 

 which was in various stages of degeneration. The 

 endometrium showed typical regressive changes 

 with hyalinization, chronic inflammation, and 

 hemosiderin. These features will also allow 

 categorization of uteri from females with un- 

 known reproductive state in future studies. Of the 

 58 animals with macroscopically diagnosed cor- 

 pora lutea and no detectable pregnancy, only 43 in 

 fact had an active corpus luteum, the remaining 

 15 specimens had corpora albicantia in various 

 stages of regression. Three corpora lutea were on 

 the right, the remaining 40 were on the left, con- 

 firming the usual finding of Cetacea that the left 

 side predominates in reproduction. When a corre- 

 lation was sought between the development of the 

 corpus luteum and endometrial changes a well- 

 delineated cycle of proliferation and edema to se- 

 cretory stages emerged. No changes indicative of 

 early pregnancy were seen and three intact uteri 

 contained no embryos. Thus, clearly, ovulation 

 does occur without pregnancy ensuing. In three 



526 



