134 THE PHYSIOLOGY OF REPRODUCTION 



vascularity or a greater quantity of liquor folliculi. 1 In this animal 

 the process must be due to a nervous reflex, induced by the act of 

 copulation. Robinson' 2 states that in the ferret ovulation is due 

 to the formation of a secondary liquor folliculi which makes its 

 appearance in the epithelial cells surrounding the ovum and which 

 follows successful insemination. The process is unaccompanied by 

 bleeding. According to Stockard 3 ovulation is caused by congestion 

 of the theca interim, but as has been shown above, in those animals 

 in which the ova are discharged spontaneously, this usually occurs 

 during osstrus, and not during the proo2strum when the congestion 

 of the generative tract is at its height. Moreover, as described 

 lelow, congestion and haemorrhage into the cavity of the follicle 

 in the rabbit may occur without rupture, the ovum and epithelial 

 cells being retained and eventually undergoing atrophy. Further- 

 more, Schochet 4 has expressed the view that ovulation is not 

 mechanical or due to pressure, but occurs as a result of digestive 

 action on the part of the liquor folliculi. 



Harper's experiments 5 on the fertilisation of the pigeon's egg 

 elucidate the question somewhat further. This author writes as 

 follows: "When a pair [of pigeons] ready for mating is put together, 

 egg-laying ordinarily ensues at the end of a rather definite period, 

 at the least eight days. The female functions are held in abeyance 

 till the proper stimulus is received from a mate. The maturing of 

 the egg is so exclusively a female function that it seems odd at first 

 thought that an apparent exception should occur to the rule. Of 

 course, we know that the final maturation of the egg, or the giving 

 off of the polar bodies, awaits in most animals the act of fertilisation. 

 But here the effect is produced upon the egg by the entrance of 

 sperms. How mating and the act of copulation [which is repeated 

 at frequent intervals every day at this time] could influence the 

 ripening of the egg in the ovary is another problem. In this 

 connection the curious fact must be mentioned that two female 

 pigeons placed in confinement may both take to laying eggs. 7 The 



1 It has been suggested that the follicle may rupture as a result of the 

 breaking down of the blood-vessels in its wall, and the consequently increased 

 pressure due to the bleeding into the cavity. See Heape. 



- Unl.inson, lo<\ '-if. 



3 Stockard and Papanicolaou, "The Existence of a Typical (Estrous Cycle in 

 tin- (Jninea-pijr," AIMT. Jour, of Ai>"(., vol. xxii., 1917. 



' Scli(K.-het, "A Suggestion as to the Process of Ovulation and Ovarian Cyst 

 Formation," Aunt. /,'.-,//, vol. x., 1916. 



Harper, "The Fertilisation and Early ] >evelopment of the Pigeon's Egg," 



JO-IT, <>f An<it., vol. iii., 1904. 



' In the rommoti fowl, and probably in most other birds, ovulation takes 

 place independently of the male. 



I am informal l.y an i-\]x-rit'nced breeder of pigeons that if overfed an 

 isolated female may lay a few eggs in the course of a year. 



