FIN CL. 

 FIN CA 

 BLUE CL. 

 SPEFIM CL. 



12 IOO 



35 8 DISCOVERY REPORTS 



In further discussions of the size of the corpora lutea and corpora albicantia the mean diameter will 

 be used as a measure of size instead of weight both because of its smaller variability and because there 

 are many more records of diameter than of weight. This applies especially to the corpora albicantia 

 which, being usually embedded in the ovary, are difficult to weigh accurately. 



Morphology 



The various morphological types of corpora lutea are illustrated in Text-fig. 5 and PI. IV, fig. 1 . The corpus 



almost invariably protrudes from the surface of the ovary and is sometimes connected only by a narrow 



neck of tissue (as in Text-fig. 5 k, I). This is probably related to the relatively rigid fibrous structure of the 



stroma, for in the smaller sperm-whale and pilot-whale 



ovaries, which are less fibrous, the corpora lutea do not 



usually protrude so much. The overall shape of the 



corpus is spheroidal and some are flattened, with an oval 



cross-section. The point of rupture of the original 



follicle is usually visible as a small stigma, surrounded 



by a corona of everted pinkish-yellow tissue, which is 



usually about 2-4 cm. in diameter. In sections the 



luteal tissue is seen to be tortuously folded and tightly 



packed, as if Text-fig. 5 b had been tightly compressed. 



This meandrine appearance is due to the initial folding 



of the follicle wall and the growth of fibrous trabeculae, 



which carry the blood vessels supplying the gland. The 



central cavity is compressed at an early stage to a thin 



slit. The fibrin in this slit is replaced by connective tissue 



so that septa ramify throughout the gland in a pattern 



complementary to the trabeculae formed by ingrowth 



of the theca externa. These internal connective tissue 



septa have no blood vessels PI. IV, fig. 2. 



The most commonly formed corpora lutea are types c, d and e in Text-fig. 5. Together they con- 

 stitute 70% of a sample of 88 fin-whale corpora in which the morphology was noted. Types d and e 

 are the most common, comprising 48% and type c, in which there is a stigma but no corona, com- 

 prises 22%. The next most abundant type are corpora lutea in which the central cavity has not been 

 completely obliterated after ovulation (types h-k). In this small sample 17% were of this type. In 

 a larger sample of 107 vesicular corpora lutea the cavity varies in size from 3 mm. to 13-3 cm. in 

 diameter. The larger corpora lutea have the larger vesicles, the mean cavity diameter increasing from 

 i-8 cm. at a corpus diameter of 7-8 cm. to 4-1 cm. at a corpus diameter of 14-15 cm. (Text-fig. 9). 

 The cavity is filled with gel, fluid, or fibrin strands and bounded by a thick layer of avascular hyaline 

 connective tissue. 



Another type is the everted corpus luteum. In these corpora the corona maybe equal to (Text-fig. 5/) 

 or greater than (Text-fig. 5^) the mean diameter of the corpus luteum. The largest corona measured was 

 12-3 cm. in diameter (from a corpus luteum 13-3 cm. in diameter) and the second largest was 10-5 cm. 

 across. The first, partially everted, type accounts for 8 % of this sample and the fully everted type for 

 3 %. The least common type is very similar to the cavitate bodies, but the stigma is widely open, there 

 is no gel or fluid and the hyaline inner wall is usually very thick (Text-fig. 5/). Only 2% (two cases) 

 of the corpora in this sample were of this type, and the true percentage in a larger sample would be 

 very small because if observed in the course of routine slicing this shape has invariably been noted. 



3 4 S 6 7 9 IO 



DIAMETER IN CMS. 



Text-fig. 8. Relation of weight to diameter for whale 

 corpora lutea and corpora albicantia (fin whale mean 

 values; other species, single records). 



