GRAAFIAN FOLLICLES 35i 



Ovarian cysts 

 Cystic follicles are of common occurrence in the ovaries of fin whales taken in the Antarctic and may 

 be up to 9 cm. in diameter. 



Other cyst-like structures also occur, very infrequently, and may be termed ' ovarian cysts ' ; they 

 are aberrant cystic follicles and it is difficult to find an exclusive definition for them. Usually, they 

 may be distinguished from true cystic follicles because their walls are either unusually thin or un- 

 usually thick, and the contents may be either fluid, gelatinous, or paste-like. Out of over 2000 ovaries, 

 ovarian cysts occurred in three immature females, 11 pregnant, eight 'resting' and one lactating 



female. 



The largest, from an immature female, was fluid-filled, 35-5 cm. in mean diameter, and weighed 

 4-3 kg. It was thick-walled and abundantly supplied with blood vessels. Another, from a 'resting' 

 female was 16 cm. in diameter and weighed 0-9 kg. Other large cysts were from a lactating female 

 (20 cm.) and three pregnant females (14, 20 and 21 cm.). The smallest, from a pregnant female, was 

 2 cm., fluid-filled, with a fibrous wall 8 mm. thick. Four cysts from 7 to 20 cm. in diameter had 

 either fluid or gelatinous contents and a peripheral layer of luteal tissue 7-10 mm. thick. Two of these 

 were from ' resting ' females and two from pregnant females. The abnormal fin-whale ovaries con- 

 taining 10 bodies superficially like corpora lutea, but composed of white fatty tissues and measuring 

 from 8 to 30 cm. in diameter, have already been mentioned (p. 343). On one of these ovaries there 

 was a 12-cm. fluid-filled cyst. One 5-4-011. cyst from a 'resting' female was similar in external 

 appearance to a corpus luteum, but contained a thick brown paste. Follicles with a cellular internal 

 structure, like an agglomeration of bubbles, are occasionally seen. 



Conclusions 

 There are insufficient data from the examination of the follicles of fin whale females taken in the 

 Antarctic to establish the variation of follicular activity during the lactation and ' resting ' phases of 

 the annual cycle, but what little there is suggests that there is a period of follicular development in 

 early lactation and another immediately after lactation. In the humpback whale, in which lactation is 

 prolonged over io| months, this post-lactation ovulation usually coincides with the male sexual 

 season and initiates the next pregnancy. 



An observation by Chittleborough (1958) is of especial interest in connexion with a possible post- 

 partum ovulation period. In one pregnant humpback female in late pregnancy (foetus 3-92 m.) the 

 follicles had developed considerably and one follicle, 48 mm. in diameter, was maturing. The corpus 

 luteum of pregnancy was in the early stages of resorption, similar in size and structure to the condition 

 normally found during early lactation. This condition is rare ; in over 70 other females during advanced 

 pregnancy there was no such marked resorption of the corpus luteum and no follicular development. 

 This exception strongly suggests that when the suppressing effect of the corpus luteum and placenta 

 is removed after parturition, there may be a post-partum follicular cycle. Marshall and Moir 

 (1952) review work in this field and show that the oestrogen content of blood and urine in the 

 human female increases during the second part of pregnancy to a maximum just before parturition. 

 The concentration rapidly falls at parturition so that after 3-4 days it has reached the level for non- 

 pregnant females. This oestrogen is mainly secreted by the placenta. It is well known that oestrogen 

 suppresses follicular growth. 



The data from pregnant females lends itself more readily to treatment because it is possible to 

 subdivide the sample and compare the variation in follicle sizes over a period of 1 1 months. It is then 

 apparent that there is a single cycle of follicular development during pregnancy. It is now generally 



