RECENT RESEARCHES ON OOGENESIS. 591 
Recent Researches on Oogenesis. 
By 
Arthur Thomson, 
I. Potar GLosBuLes AND ExtRusIONS FROM REPRODUCTIVE 
CELLs. 
In Balfour’s convenient summary, which may be regarded 
as representing the state of scientific knowledge in 1880, 
polar globules are defined as one or two cells which appear 
on the surface of the ovum before or after fertilisation, and 
which arise by a regular process of division from the ger- 
minal vesicle. As to their physiological import it is further 
suggested that in their extrusion certain important con- 
stituents are removed from the germinal vesicle, without 
which it is incomplete and incapable of further development, 
unless these are again supplied by the spermatic nucleus, but 
retaining which the ovum is capable of developing partheno- 
genetically. The somewhat too teleologically-expressed obser- 
vation ‘‘that the function of forming polar cells has been 
acquired by the ovum for the express purpose of preventing 
parthenogenesis,” is supported by reference to the fact that 
parthenogenesis is specially characteristic of Arthropoda and 
Rotifera, “the only two groups in which polar bodies have not 
so far been satisfactorily observed.” 
In attempting to summarise the most important recent 
researches on the history and nature of polar globules, it will 
be convenient to report these as they concern (1) the occur- 
rence and history of polar cells, and of other extrusions from 
the reproductive cell; (2) the morphological import of these 
bodies ; and (3) their physiological rationale. 
