Apeil 29, 1921] 



SCIENCE 



421 



less. One or two days before the onset of 

 oestrus some of tlie follicles rapidly enlarge 

 to the full diameter of 7 to 10 mm., and the 

 enclosed ova pass through the preliminary 

 stages of maturation. Ovulation occurs on 

 the second of tlie three days of oestrus; the 

 ova are three days en route through the 

 Fallopian tube and pass into the uterus on 

 the fourth day. If not fertilized they degen- 

 erate in utero about the seventh or eighth 

 -lay after ovulation. The corpora lutea, as 

 ai.-eady described, reach full histological com- 

 plexity about the seventh day, by which time 



oesTras 



When the pig's ova are fertilized, the em- 

 bryos gain attachment to the uterine wall be- 

 tween the tenth and fifteenth day after 

 ovulation. It is a most important fact, there- 

 fore, that the corpus luteum persists until 

 the fourteenth or fifteenth day, for this find- 

 ing harmonizes with the current hypothesis 

 that the corpus luteum exercises an effect 

 upon the uterus, preparing it for implanta- 

 tion. The duration of the corpus luteum is 

 quite variable in different sx)ecies, but in none 

 has it been found less than the time required 

 for attachment of the embryos. Another sup- 



oestru.5 



DAYS O Z ^6 a 10 IZ n iB la ZO ZZ 2/i- Z6 Za 30 32. Ji 



Fie. 1. 

 Diagram representing the ovarian cycle of the nonpregnant sow. 



they have attained a diameter of 9 mm. The 

 new specimens show that they remain in a 

 state of full development, without obvious 

 further change, until the fourteenth or 

 fifteenth day after discharge of the follicles, 

 and then begin a retrogression which is 

 initiated by a sudden disintegration of the 

 granulosa lutein cells, which have formed the 

 chief bulk of the organ. In a few days more 

 the corjKJra consist only of connective tissue 

 containing in its meshes a few lipoid-laden 

 cells; and by the time of the next ovulation 

 they have diminished in size to a diameter of 

 6 mm. During the second interoestral interval 

 after their formation they shrink still further, 

 until at the age of 40 days they are but 2 or 

 2.5 mm. in diameter. After this they are not 

 readily distinguishable from other ovarian 

 tissues in the gross, and microscopically are 

 so far degenerated that one does not feel able 

 to separate them from atretic follicles. 



position with regard to the function of the 

 corpus luteum, that it serves, while present, 

 to restrain the growth of follicles, is also 

 borne out by our observations, as far as they 

 go, for it will be noticed that a new group of 

 follicles passes beyond the resting dimension 

 only after the degeneration of the last corpora 

 is under way. 



A full account of these studies will form 

 part of a monograph on cyclic changes in the 

 ovaries and uterus of the pig, now in prepara- 

 tion. 



George W. Corner 



Johns Hopkins Medical School 



THE NATIONAL ACADEMY OF 

 SCIENCES 



The annual meeting of the National 

 Academy of Sciences was held at the N^atural 

 History Building, U. S. National Museum, in 

 Washington on April 25, 26 and 27, 1921. 



