304 EDGAR ALLEN 
but considerably lower than that of the vagina, is continued up 
into the cervix in virgins as well as in multiparae, but beginning 
at the branching of the cervical canal, it becomes simple, non- 
ciliated, cuboidal or columnar. Glands are uniformly distrib- 
uted throughout the uterine mucosa except along the line of 
attachment of its broad ‘mesentery-like’ ligament. The entrance 
of the oviduct into the uterine cornu is surrounded by valve- 
like folds of the mucosa, which make it very difficult to inject 
the oviducts from the uterus. These valves are in a position to 
guard against a back flow of fluid from the distended uterus into 
the oviducts, which might be fatal to the passage of ova down 
the tubes. The oviducts are ciliated only at the ovarian end 
where the mucosa is thrown into high folds. Throughout the rest 
of their extent the epithelium is simple columnar. The uterine 
end can be distinguished from the middle segment by the low 
folds of its mucosa, those in the middle segment being rela- 
tively high. 
The ovaries are situated just caudad to the kidneys and are 
completely surrounded by closed sacs of peritoneum from which 
the openings of the oviducts lead. Therefore, the number of 
ova in the tubes and periovarian sacs is always the number 
ovulated, since none can escape into the peritoneal cavity. 
4, EXTERNAL MORPHOLOGICAL CHANGES DURING THE OESTROUS 
CYCLE 
a. Evidence from the external genitalia and cell contents of 
the vagina. Among many rodents there is very little or no 
discharge during ‘heat.’ The degree to which congestion and 
reddening occur in the vulva is also variable, often being totally 
absent or so slight as to be a very poor criterion of oestrus. In 
a total of 355 cycles chosen at random to decide this point in 
the mouse, only 190, or 53.5 per cent, showed well-marked ex- 
ternal signs. And seventy-three, or 23.3 per cent, showed the 
vulva and vagina in an apparently resting condition, although 
by the cell contents of the vaginal fluid oestrus was shown to 
be present. A few animals evidenced continued external signs 
of ‘heat’ during the metoestrum and the dioestrous interval, so 
