1910-11.] Development of Germ Cells in Mammalian Ovary. 157 
The physiological function of the nucleoli is still involved in doubt, but 
there is strong evidence to prove that they do not contribute to the forma- 
tion of the chromosomes. Moore and Robinson (17) have investigated the 
behaviour of the nucleolus, and find that it has much the same function as 
the nucleolus of the somatic cell. 
Part III. — Present Investigation. 
A. Material and Methods. 
As the work of v. Winiwarter and Miss Lane-Claypon had been done 
on the rabbit, it was on the lines of their work that I first began my inves- 
tigation. After working for some months on the rabbit embryo I abandoned 
this material, as the differentiation of the various structures in the ovary 
was not marked, the germ cells being small in size and their nuclear changes 
difficult to follow. For this reason, and also with the hope that fresh 
observations on parallel mammalian types would prove of more value, I 
carried out the investigation on the pig and human embryos, and the 
kitten and puppy for post-natal changes. In this way a plan of develop- 
ment has been formed by a comparison of the growth of the ovary in all 
these types, and conclusions have been arrived at which are in agreement 
with those of the majority of previous investigators. Some points in 
the development of the germ cells of the kitten and puppy differed from 
those recorded by v. Winiwarter in 1900. These points I demonstrated 
before the Physiological Section of the British Medical Association, July 
1909. I find in the recent papers of v. Winiwarter and Sainmont (to which 
I have only had access within the last few months) that they have found 
the same changes in the kitten’s ovary as I have found. The stages of the 
pig embryo were taken according to the measurements of the length of the 
embryo, as no approximation of the gestation period could be arrived at 
with accuracy ; and as the embryo nearest the mesial portion of the uterus 
is more advanced in growth than that further away, the length measure- 
ment is the only accurate one to be used. 
Embryos of 6, 8, 10, 12, 13, 14 cm. were examined, and finally 16-18 
cm., the stage just before birth. The human foetal ovaries were taken at 
the 4th, 5 th, 6th, 7-7 J months, and the new-born. The puppies obtainable 
were new-born, 10 days after birth, 3 and 4 months. The kittens were 
17 days, 4, 6, and 10 weeks. The examination of the rabbit’s ovary was 
made on embryos of 21 and 26 days, at birth, 4 days after, and 4 months. 
The ovary of a new-born lamb was also investigated. 
Methods . — For the young embryo the abdominal cavity was opened and 
