TYPES OF (ESTROUS CYCLE 31 



consists of leucocytes with only a few cornified cells. Imme- 

 diately after this, nucleated epithelial cells appear again. 

 During dicestrus the vaginal smear consists of nucleated 

 epithelial cells with a number of leucocytes. The opossum is 

 remarkable in having lateral vaginal canals which undergo a 

 similar cycle. 



The mammary glands of the opossum have a very clear cycle. 

 Growth begins at prooestrus, and continues uniformly until the 

 end of pseudo-pregnancy or the end of true pregnancy. It is 

 necessary to suppose that the beginning of this growth is under 

 the control of the oestrus-promoting stimulus and that later the 

 corpora lutea are responsible. The growth occurring during 

 prooestrus is, however, comparatively slight compared with that 

 found during pseudo-pregnancy. At the end of pseudo-preg- 

 nancy or true pregnancy, atrophy sets in, and the lowest point 

 of development is reached about twenty-three days after the 

 previous ovulation or some live days before the next ovulation 

 is due. 



{b) DOG 



Some observations on the ovary of the dog were made by 

 Bischoff (66) as early as 1845. Bouin and Ancel (75) and Van 

 der Stricht (602) later studied the ovarian cycle. Fried- 

 laender (233) appears to have been the first to deal with 

 the uterine mucosa, while Retterer (533) and Keller (319) 

 published more detailed work. The whole subj ect of the oestrous 

 cycle in the dog has been investigated in detail by Marshall and 

 Jolly (450), Marshall and Hainan (449), and more recently by 

 Gerlinger (240, 241) and Evans and Cole (185). 



With the exception of the vagina, the cyclic changes in the 

 reproductive organs are very definite. During anoestrus, the 

 ovary is small and contains neither large follicles nor functional 

 corpora lutea. Primordial follicles are, however, developing. 

 The uterus is thin and anaemic. The mucosa is shallow, and the 

 glands and vessels are few. Prooestrus is characterized by 

 follicular growth in the ovary, while thickening of the mucosa, 

 accompanied by congestion and multiplication of the stromal 

 capillaries, takes place in the uterus. The glands of the mucosa 

 begin to secrete. According to Marshall and Hainan, the 



