548 Dr. F. H. A. Marshall and Mr. E. T. Hainan. 



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- 

 corpora lutea of pregnancy. It is equally evident, however, that in moncestrous 

 animals, such as the Dog, the persistence of the corpus luteum spurium over 

 a considerable period would not exercise the same prejudicial effects as in 

 polycestrous animals. 



It became of interest therefore to ascertain the duration of the corpus 

 luteum spurium in the Dog, and to discover whether, if this organ persists 

 for a longer period than in polyoestrous animals, the continuance is associated 

 with uterine and mammary development comparable to what occurs in the 

 pseudo-pregnant Eabbit and in the Marsupial Cat. Accordingly we took a 

 number of bitches (mostly virgins) which were not permitted to become 

 pregnant, and killed them at varying intervals after " heat," so as to acquire 

 a series of stages showing different degrees of development in the generative 

 organs and mammary glands. . 



The animals were kept under observation for prolonged periods, and there 

 could be no doubt about the occurrence of the " heat " periods from which the 

 stages of development were dated, for in each case there was a very definite 

 sanguineous discharge of normal duration. Certain of the bitches, however, 

 had at previous times shown very slight indications of heat, as manifested by 

 congestion of the vulva accompanied by a mucous discharge. In view of 

 these observations, little or no importance should be attached to the 

 transitory appearances suggestive of heat which have been recorded as 

 occurring after the injection of ovarian extracts* (Marshall and Jolly). 



The following are the records of the cases dealt with in the present 

 investigation : — 



(1) A half-bred Whippet (a virgin) began to show pro-cestrous bleeding 



from the vaginal opening on May 17. It stopped bleeding on May 31. On 



June 2 it was killed, and the generative organs and portions of tissue from 



the mammary region were preserved. The right ovary contained three 



discharged follicles, and the left ovary two. Sections through the discharged 



follicles showed that they were of very recent origin, ovulation having taken 



place probably within the previous two days. The corpora lutea were not 



organised, the ingrowth of connective tissue from the follicular wall was 



relatively slight, the cavity was only very partially and irregularly filled in, 



* In a former investigation by Carmichael and Marshall, experiments with com- 

 mercial ovarian extracts were entirely negative. The transplantation experiments 

 by Marshall and Jolly, upon which the views put forward were mainly based, belong 

 to a different category, for in these cases heat of normal duration and character 

 occurred. Transient signs of heat were never observed after ovariotomy had been 

 performed. 



