134 CYCLIC CHANGES IN THE OVARIES AND UTERUS OF THE SOW, ETC. 



or by parturition; whereas the theca interna cells, presumably derived from the 

 ovarian stroma, behave as if morphologically part of the somatic ovarian tissues, 

 only temporarily bound up with the fortunes of the ovum. It is to be hoped that 

 this conception may be tested by work on other species. 



Text-figure 2 gives, in diagrammatic self-explanatory form, a picture of the 

 ovarian cycle as we have described it in the foregoing pages. 



OESTRUS 



OESTRUS 



10 12 14 16 18 20 22 24 26 28 JO 32 34 36 36 40 42 



OESTRUS 



II- 

 10 

 9- 

 8- 

 7- 

 6- 

 5- 

 4- 

 3- 

 Z- 



F 



P R E G NAN C V 



ALLANTOIS EXPANDED 



I i >("("( i i i i i i i i i i i i j ii I I r i r I I r r-i I r i I i i i i i i I ii i I i 



DAY5 Z 4 6 B 10 12 14 16 18 20 12 24 26 28 30 i2 34 36 16 40 42, ere. 



Fio. 2. Diagram showing in graphic form the relations between oestrus, ovulation, the development 



of the. corpus luteum, and the progress of the ova in the aow. 

 Above: events of the average cycle of 21 days in the non-pregnant sow. 

 Below: events of the first weeks of pregnancy. 



