

395 
Contributions to the Physiology of Mammalian Reproduction. 
Part L—The CMstrous Cycle in the Dog. Part Il—The 
Ovary as an Organ of Internal Secretion. 
By Francis H. A. MARSHALL, Carnegie Fellow in the University of Edin- 
burgh ; and WILLIAM A. JOLLY, Assistant to the Professor of Physiology 
in the University of Edinburgh. 
(Communicated by Professor E. A. Schafer, F.R.S. Received May 13,— 
Read May 18, 1905.) 
(Abstract. ) 
PART. 
The Cistrous Cycle in Carnivores.—The bitch is moncestrous and has typi- 
cally two sexual seasons in the year. The wild species of the genus in their 
natural state have only one sexual season annually, but in captivity they may 
experience two sexual seasons like the bitch. The Cape hunting-dog (Lycaon) 
in captivity has been shown to come on heat usually only once a year. 
The domestic cat has three or four sexual seasons in the course of the year. 
We find also that it is polycestrous and may have four heat-periods in a single 
sexual season. The duration of the dicestrous cycle is about a fortnight. 
The wild cat probably experiences only one sexual season in the year. The 
male possesses a rutting season. 
The lioness, failing pregnancy, may have several annual sexual seasons, at 
the same time being polycestrous. The duration of the dicestrous cycle is 
said to be three weeks. Bears, polecats, and seals, and probably most other 
carnivores, appear to be moncestrous and breed once a year; but the otter, in 
captivity at any rate, is polycestrous, having a continuous series of dicestrous 
cycles, each of a month’s duration. 
The periodicity of cestrus is dependent to some extent upon environ- 
mental conditions as illustrated in the case of the fox. Domestication and 
captivity appear to favour increased frequency in the recurrence of the cycle. 
The Histology of the Uterus during the Cycie—The histological changes 
which the uterus undergoes may be divided into the following periods :— 
GiMEerIOd Of TESts... 665. foce. icc dee ee cees Ancestrum. 
2 th estion ... 
(2) if erow a congestion ean 
(3) % Gesteuction i...2c.0.65000. 
; (Hstrus. 
(4) oe FOCUPCMALION .......+--+08: 
~ Metoestrum. 
