172 Prof. F. 0. Bower. Studies in the [June 15, 



1. Ovulation does not necessarily occur during each, menstrual 



period, and 



2. That menstruation is not brought about by ovulation. 



The two corpora lutea seen occurred in specimens of Stage III and 

 Stage IV ; during these stages the first great increase of the blood 

 supply to the mucosa takes place, and it therefore appears possible 

 that the increased supply of blood to the generative organs during 

 the early stages of menstruation may possibly induce ovulation when 

 a sufficiently ripe ovum is present in the ovaries; there is direct 

 proof, however, that an ovuin is not dehisced at each menstrual 

 period. 



Conclusion. 



Recent observations show that periods of growth and degene- 

 ration occur in the mucosa of the bitch when rutting, but de- 

 nudation is not described. There is good reason to believe that 

 the period of growth is invariably present in the mucosa of rutting 

 animals, and, as ovulation and rut are stated to be coincident, it 

 appears highly probable that the period of growth during menstrua- 

 tion represents the preparation of the mucosa for the reception and 

 retention of an ovum, while the degeneration period represents the 

 result of failure to fertilise the ovum or failure of ovulation. 



I venture to express the belief that the function of menstruation 

 may be thus expressed, but I fail to find any evidence of the origin 

 of menstruation. 



Note. Since the above was written, I have seen Marshall's book 

 on 'Vertebrate Embryology' (1893), in which he also divides the 

 phenomena of menstruation into four stages, identical with my four 

 Periods A, B, C, and L). The arrangement was arrived at inde- 

 pendently. 



XV. " Studies in tbe Morphology of Spore-producing Members. 

 Part I. Equisetinese and Lycopodineae." By. F. 0. BOWER, 

 D.lSc., F.R.S., Regius Professor of Botany in the University 

 of Glasgow. Received June 9, 1893. 



(Abstract.) 



Two preliminary statements have already been communicated on 

 this subject (' Roy. Soc. Proc.,' vol. 50, p. 265, and vol. 53, p. 19), deal- 

 ing with some of the observations made during work extending over 

 more than four years. 



The paper which I now submit to the Society includes the de- 

 tailed statement of results acquired from the Equisetineee and Lyco- 

 podineaa. 



