CHANGES IN THE OVARY 131 



Longley has shown that in the cat ovulation takes place only 

 after coition.^ 



Artificial insemination, followed by pregnancy, has been success- 

 fully performed on mares, donkeys, and cows.'' Consequently it may 

 be concluded that these animals ovulate independently of coition. 

 According to Ewart,^ ovulation in the mare very often does not occur 

 until near the end of the oestrous period. 



It has been shown also that the sheep ovulates spontaneously at 

 each of the earlier heat periods of the sexual season, but that there 

 are reasons for believing that during the later periods the stimulating 

 power- at the disposal of the ewes may be so reduced that without 

 coition it is incapable of causing ovulation. There is also evidence 

 that when coition occurs at the beginning of an oestrous period, it 

 may provide a stimulus inducing ovulation to take place a few hours 

 earlier than it otherwise would; in other words, that if ovulation 

 has not already occurred during an oestrus, the stimulus set up by 

 coition may hasten the rupture of the follicle.* Eecently Iwanoff 

 has succeeded in inducing pregnancy in sheep by artificial insemination. 

 (See p. 176). 



There can be little doubt that in the great majority of Mammals 

 ovulation, as a general rule, occurs regularly during oestrus. In 

 certain bats, however, copulation is performed during the autumn, 

 whereas ovulation is postponed until the following spring, the animals 

 in the meantime hibernating, while the spermatozoa are stored up in 

 the uterus (see p. 170).^ The ovary in the winter months (during 

 the hibernating period) is said to be in a state of quiescence, and the 

 exact time for maturation and ovulation depend upon the temperature 

 of the early months of the year, occurring generally in February or 

 March, but sometimes as late as April.^ Ovulation takes place some 



1 Longley, " Maturation of the Egg and Ovulation in the Domestic Cat,' 

 Amer. Jour, of Anat, vol. xii., 1911. Doncaster has recorded that a female oat, 

 after copulating with a sterile tortoiseshell male, secreted milk about four weeks 

 later, and continued to do so for two weeks, but without experiencing pregnancy. 

 This was clearly a case of pseudo-pregnancy comparable to what occurs in 

 Basywrus, the dog, and the rabbit under experimental conditions. See p. 36. 

 ("A Possible Connection between Abnormal Sex-limited Transmission and 

 Sterility," Camh. PhU. Soc. Proc, vol. xvii., 1913.) 



^ Heape, "The Artificial Insemination of Mammals," Proc. Roy. Soc, vol. 

 Ixi., 1897. There is direct evidence of spontaneous ovulation in cows. 



' Ewart, " Studies on the Development of the Horse," Traris. Roy. Soc. Edin., 

 vol. li., 1915. 



* Marshall, "The CEstrous Cycle and the Formation of the Corpus Luteum 

 in the Sheep," PhU. Trans., B., vol. cxcvi., 1903. 



° Benecke, " Ueber Keifung und Befruchtung des Eies bei den Fleder- 

 mausen," Zool. Anz.,' vol. ii., 1879. Eimer, "Ueber die Fortpflanzung der 

 Fledermause," Zool. Anz., vol. ii., 1879. Van Beneden and Julin, "Observa- 

 tions sur la Maturation, la F^condation, et la Segmentation de I'CEuf chez les 

 Cheiroptferes," Arch, de Biol., vol. i., 1880. 



' Van der Stricht, "L'Atr6sie ovulaire, etc.," Verhand. d. Anat. Gesell. in 

 Bonn, 1901. Les Mitoses de Maturation, etc., Nancy, 1906. 



