22 EDWARD MCCRADY, JR. 



of fertility was as bad in matings before 7 as it was in those 

 after 7. As the real number of matings was probably much 

 less than the computed maximal possible number, the real 

 percentage of fertility must be very much higher in the earlier 

 matings. 



A possible explanation is that ovulation and oestrus both 

 usually occur in the early morning hours (i.e., before 7), and 

 that when mating is delayed it usually means that oestrus is 

 late with reference to ovulation, and correspondingly the 

 sperm reach the ova too late for fertilization. Usually only 

 unfertilized ova are found in females which have been seen to 

 mate after 7. 



All the ova from one ovary are discharged simultaneously, 

 and both ovaries ovulate together. The average number of 

 eggs from each ovary at each ovulation is eleven (Hartman, 

 '19), though as many as twenty-two from each ovary have 

 been recorded. 



Mature spermatozoa may be found in testes at any time of 

 the year, but maturation stages are more abundant at the 

 beginning of the breeding season (Painter, '22). The male 

 is. probably capable of fertile coitus at any time, but is 

 aroused to activity only by the 'heat' of the female. 



During copulation the penis (fig. 4) passes directly into the 

 urinogenital sinus (fig. 5). The glans of the penis is bifid, 

 but the urethra opens between, not at the tips of, the prongs. 

 However, a groove, which is very nearly converted into a tube 

 by its overhanging edges, extends along the medial side of 

 each prong for more than half of its length. It is possible that 

 these grooves serve in place of a bifid urethra to carry the 

 semen directly into the lateral vaginal canals. 



These latter organs show a considerable muscular activity 

 during oestrus (Hartman, '24). By alternate contraction 

 of their proximal and distal portions they churn the liquid 

 within them. When semen is introduced into this liquid two 

 things happen. In the first place, some spermatozoa are de- 

 livered to the os uteri almost immediately by the currents set 

 up by the churning. And in the second place, a coagulation 



