ii8 CYCLIC CHANGES IV 



ovipositor. In this way, coordination between (i ) the hypo- 

 physis, (2) the gonad, and (3) the ovipositor became 

 apparent. 



a. Inter-estrus. The central point of sexual life is the 

 maturation of the ovum. Pevelopment of the ovum and 

 formation of the corpus luteum have already been described 

 cytologically (p. 77). We shall now, therefore, deal mainly 

 with statistical data concerning the ovary. In the month of 

 July following the last oviposition, maturing and mature 

 oocytes (i 100 — 2000 11) are absent from the ovary, having 

 been discharged. Apart from a small number of medium- 

 sized oocytes (200 — 500 jli) , the ovary now contains a very 

 large number of small oocytes (10 — 200 ju), as seen in the 

 ovary of a young animal (Fig. 77A). This condition lasts 

 only a short time, for in the same month medium-sized ova 

 develop from this reservoir of small oocytes, and they in turn 

 give rise to larger ones. It is probable that this growth of 

 gametes is initiated by the hypophysis. During the autumn 

 and winter the formation of medium-sized ova from smaller 

 ones proceeds slowly, while the number of large ova remains 

 at the same level. These large cells, however, also grow 

 slightly during this time, i.e., from 500 to 800 jn (Fig. 77A). 



b. Pro-estrus. By the end of the winter (February) the 

 ovary possesses a few small oocytes, and a large number of 

 medium-sized ones. During the next 2 months of pro-estrus 

 the number of medium-sized oocytes diminishes rapidly with 

 the formation of pre-ovulation corpora lutea (Fig. 77B). 

 Even large-sized oocytes participate in this change. The 

 abundant pro-estrous formation of corpora lutea, however, 

 is not accompanied by an equally intensive growth of the 

 ovipositor, as might be expected (Fig. 77C). From February 

 to April the ovipositor shows only slight growth, during 

 which the tissue gradually begins to respond to successive 

 hormonal stimuli, until, during estrus, the normal degree of 

 sensitivity is reached. The corpora lutea in pro-estrus, there- 

 fore, it is suggested, sensitise the ovipositor. A further charac- 

 teristic of this period is an intensive growth of the large 

 oocytes into maturing ones of 2000 /li. 



