OVARIAN FOLLICLES IN FERRETS AND FERRET-POLECAT HYBRIDS. 307 
Description. 
In the course of the observations upon the growth of the ovarian follicles of the 
ferret and other phenomena associated with the development of the ova of ferrets 
certain points have been noted which have little or no direct bearing upon the 
question at present under consideration ; they are perhaps not of sufficient importance 
to justify a separate communication, but they have a certain amount of morphological 
or histological interest, and to these points attention will be directed, incidentally, 
in the course of the description. 
The Ovaries. 
The ovaries of ferrets are of irregular ovoid form, the cranio-caudal length 
always exceeding the dorso-ventral and the side-to-side measurements, and, as 
a rule, but not always, the dorso-ventral diameter exceeds the side-to-side 
measurement. 
The size of the ovary naturally varies at different periods ; it is smallest in the 
anoestrus period, and largest about the middle of pregnancy ; the average size, 
measured upon 366 ovaries taken from 183 animals killed between the early part of 
November and the middle of July, measured, after fixation and hardening, and stated 
in cubic millimetres, was 30’095996866 mm. 3 , the smallest ovary of the anoestrus 
period being 9 mm. 3 , and the largest 44 mm. 3 There is some relationship between 
the weight of the animal and the size of the ovary, but it is by no means constant, 
and the smallest ovary, 9 mm. 3 , was obtained from an animal which weighed 19 
ounces, whilst ovaries of double that size were obtained from animals weighing only 
16 ounces. 
The average size of twenty ovaries, taken from ten anoestrus ferrets, killed in 
November, December, and January, was 20‘238 mm. 3 , and the size of the largest 
ovary taken from a pregnant animal was 66'87 mm. 3 ; it may be assumed, therefore, 
that the ovary may increase to at least three times its average anoestrus size 
during pregnancy. 
The ovaries of the left side are as a whole larger than those of the right side, 
the average size of the ovaries of the 183 animals before mentioned being 28'626 
mm. 3 , the average size of the left ovaries was 31 ‘565 mm . 3 The point is of no 
particular importance, but it is noticeable in association with the disappearance of 
the right ovary in birds, the greater size of the left ovary of monotremes, and the 
tendency, which is so constant in mammals, for the persistence of the left of any 
two organs which are formed bilaterally during embryonic life, and of which one 
disappears during development, the ventral rudiments of the pancreas being an 
exception. It must be noted, however, that in ferrets, in a proportion of cases which 
constitute somewhat less than a third of the whole, the right ovary is larger than 
the left. The difference is not due to the fixative and hardening processes, for though, 
