THE TESTICLE AND THE OVARY 373 



corpora lutea. Extirpation of the corpora lutea was followed (see 

 below, p. 620, Chapter XIII.) by an arresting effect, and by an 

 acceleration of the next ovulation.^ As long as the corpora function- 

 ate the presence of mature follicles does not produce those uterine 

 changes which are characteristic of heat. 



In polyoestrous animals the corpus luteum spurium usually 

 degenerates after a short period so as to make way for the 

 maturation of new follicles and the process of ovulation at the 

 frequently recurring oestrous periods. Otherwise the ripening 

 follicles degenerate under the influence of the corpus luteum. Thus 

 follicular atrophy occurs in widening circles around the corpus 

 luteum of Dasyurus. The more rapid degeneration of the corpus 

 luteum' spurium has probably taken place in association with the 

 acquirement of the polyoestrous habit since it would be detrimental 

 to fecundity if these structures persisted for as long a time as the 

 corpora lutea of pregnancy. 



In monoestrous animals, on the other hand,- the persistence of the 

 corpus luteum spurium over a period equal to that of pregnancy 

 would not tend towards infecundity, and this probably accounts for 

 the condition found in the dog.^ Keller* was the first to describe the 

 post-oestrous hyperplasia in the uterine glands and the retrogressive 

 stage which follows, observations which have since been confirmed 

 and extended. The epithelium of the glands, after being first 

 columnar afterwards becomes cubical, and in the retrogressive stage 

 the lumina contain a colloid and sometimes desquamated cells. 

 There is much haemorrhage in the stroma. Eetrogression sets in 

 about thirty days after ovulation, the mammary glands going through 

 a similar cycle, growth being followed by a secretion of 'fluid which 

 may be identical with milk. These changes occur in correlation 

 with the growth and degeneration of corpora lutea (see above, 

 Chapter III., p. 99). 



The corpus luteum in polyoestrous animals is known sometimes 

 to persist for an abnormal length of time, and according to Williams 

 may be a cause of long-continued sterility. Why the organ should 

 persist is not clear, but Williams * states that this condition occurs 

 most frequently in young cows or heifers which have suffered 

 some time previously from contagious granular vaginitis. In certain 



' Excision of corpora lutea in pregnancy, while promoting ovulation, is not 

 followed by a new uterine cycle, as during pregnancy a mechanism is at work 

 preventing the uterus from responding to stimuli given oif by the ovary (Loeb). 



2 Marshall and Hainan, "On the Post-CEstrous Changes occurring in 

 Generative Organs and Mammary Glands of the Non-Pregnant Dog," Froc. 

 Roy. Soc, B., vol. Isxxix., 1917. 



3 Keller, "Ueber den Bau des Endometrium beim Hunde," Anat. Hefte, 

 vol. cxviii., 1909. 



* Williams (W. L.), Veterinary Obstetrics, New York, 1917. 



