ANNUAL OVARIAN CYCLE 



feature of cyclical activity. The nuclear membrane is intact throughout the 

 entire growth period, and the chromosomes remain in a state of inactivity; 

 the behavior of the nucleoli, however, is of considerable interest. Nucleoli 

 are present in all stages of oocytic growth, their number increasing as the 

 oocyte grows. No definite cyclic change in the proportion of large and small 

 nucleoli has been noted. The most striking feature in connection with them 

 is their gradual movement from the periphery of the nucleus to the imme- 

 diate vicinity of the chromosomes. This movement begins in September and 

 is completed at the time the oocytes reach their greatest development in the 

 summer. King thought this arrangement of nucleoli in the egg previous to 

 maturation to be characteristic of all amphibian eggs. 



A careful study of the comparative sizes of oocytes from frogs of each 

 month of the year leads to the conclusions which follow. The ovaries of those 

 specimens collected from any month of the year contain oocytes of varying 

 stages of growth. The least variation is found in the ovaries during late Sep- 

 tember and October. An increase in the size of the oocytes is found month 

 by month, December excepted, until the onset of the breeding season. Sizes 

 of those fixed during the month of December, as noted previously, fluctuated 

 irregularly, although this fact is probably of little significance in the charac- 

 terization of the annual cycle. Durmg July and August the ovaries contain 

 oocytes of approximately the same average size, although more very small 

 oocytes were noted in the ovaries of frogs collected in the latter part of July 

 and in August than in the early part of July. Young oocytes which are to 

 remain in the ovaries and constitute the next generation of oocytes are seen 

 in late July and August and constitute the bulk of the ovaries in September, 

 while the well-developed oocytes in ovaries of frogs fixed during August 

 are either breaking out of the ovary or are degenerating and being resorbed. 

 Few large ones remain in a whole condition at this time. The very small ones 

 are found grouped around the periphery of the ovaries and this represents 

 the earliest period at which new oocytes are seen as they move into the ovary 

 to replace those degenerating or being lost through ovulation. The marked 

 difference between the predominant stage of oocyte growth in July and that 

 of late September clearly marks the close of the breeding season in late August 

 and early September. 



Changes in the average percentages of ovarian volume correspond quite 

 closely to other changes taking place in the annual cycle. The percentages in- 

 crease during the spring months, reaching a maximum in May, June, and 

 July. A decline begins gradually in August, which may be accounted for by 

 the occurrence of ovulation and degeneration of oocytes. Averages in the late 

 fall and winter months are the least of the year. 



A study of the length of the body, volume of the entire body, volume 

 of the ovaries, and the percentage of ovarian volume of mature females of 

 Acris suggests several general relationships. Correlation between the size of 

 the ovaries and the body length is slight, but the volume of the body, ex- 

 clusive of the ovaries, is correlated with the body length. Considerable varia- 

 tion is found among mature frogs of any month in the percentages of ovarian 



