146 THE PHYSIOLOGY OF REPRODUCTION 



who believes them to be identicat with mammalian corpora lutea. 

 It is noteworthy that the above-mentioned animals which show 

 luteal hypertrophy are all viviparous. On the other hand, Biihler, 1 

 who investigated the ovaries of Cyclostomes and certain Teleosteans, 

 was unable to find any hypertrophy of the wall of the spent follicle, 

 and Cunningham, 2 also writing on Teleosteans, arrived at the same 

 result as Biihler. According to Pearl and Boring, 3 however, a corpus 

 luteum is formed in the ovary of the hen after ovulation and simply 

 from the theca interna. It contains a yellow, fatty substance similar 

 to that of the corpus luteum of the cow. 



The mammalian corpus luteum may contain a central clot 

 composed of blood derived from the vessels of the follicular wall 

 which gave way at the time of ovulation. In this case the blood- 

 clot becomes gradually absorbed along with the remainder of the 

 liquor folliculi. On the other hand, there may be practically no 

 haemorrhage, or the discharged blood may be expelled to the exterior 

 of the ovary (with the greater part of the liquor), remaining as a 

 small clot upon the surface. 4 It would seem probable that the 

 vessels burst as an effect of the released tension consequent upon 

 the rupture of the follicle ; but, as already mentioned, it has been 

 suggested that possibly the latter process may itself occur as the 

 result of the pouring out of blood into the cavity. During the early 

 stages of formation of the sheep's corpus luteum leucocytes of the 

 polymorph variety nave been observed in great abundance, but in 

 the later stages they disappear, some of them undergoing degenera- 

 tion. These leucocytes are not extravasated, but wander inwards 

 with the growing strands of connective tissue. 5 Their occurrence 

 should probably be associated with the necessity to dispose of the 

 blood-clot when such is present. 



The ingrowth of connective tissue commences a very short time 

 after ovulation, and in the sheep may be seen very distinctly as 

 early as in the seven-hour stage of development. Blood-vessels 

 are carried inwards with the connective tissue, and these undergo 

 multiplication, so that the corpus luteum is a highly vascular structure. 



If the discharged ovum fails to become fertilised the corpus goes 



1 Btihler, "Riickbildung der Eifollikel bei Wirbelthieren," Morph. Jahr., 

 vol. xxx., 1902. 



2 Cunningham (J. T.), " On the Histology of the Ovary and of the Ovarian 

 Ova in certain Marine Fishes," Qiiar. Jour. Micr. Science, vol. xl., 1897 ; Honnoites 

 and Heredity, London, 1920. 



3 Pearl and Boring, Sex Studies : " The Corpus Luteum in the Ovary of 

 the Domestic Fowl," Amer. Jour Aiutt., vol. xxiii., 1918. 



4 It is sometimes stated that the haemoglobin of the blood clot is trans- 

 formed into the yellow pigment (known as lutein) which gives the luteal cells 

 their characteristic colour ; but this is obviously incorrect, since there may lie 

 no blood-clot in the follicle, whereas the luteal cells always contain lutein. 



6 Mai-shall, Phil. Trans., lw. dt. 



