ZOOLOGY: E. G. CONKLIN 
491 
WHY POLAR BODIES DO NOT DEVELOP 
By Edwin G. Conklin 
DEPARTMENT OF BIOLOGY. PRINCETON UNIVERSITY 
Presented to the Academy, August 3, 1915 
Since the work of 0. Hertwig (1890) and Boveri (1891) it has been 
known that the two small cells which are formed at one pole of the 
egg during |ts maturation divisions and which have long been known 
as ^polar bodies' since they mark out the ^animal' or ectodermal pole 
of the egg are homologous with ceils which in the male give rise to 
functional spermatozoa, so that the polar bodies are generally recog- 
nized as small and non-functional egg cells, a view which was first set 
forth by Mark (1881). Before the two maturation divisions which 
lead to the formation of eggs or spermatozoa the sex cells are called 
^oocytes' in the case of the female, 'spermatocytes' in the case of the 
male; after the first maturation division they are called 'second oocytes' 
or 'second spermatocytes' and after the second maturation division they 
are known as 'ootids' or 'spermatids.' In the case of the male both of 
these divisions are equal and all of the spermatids may become functional 
spermatozoa, in the female both maturation divisions are usually very 
unequal the smaller division product in each case being the 'polar 
body,' and the larger the 'egg.' 
In many animals the maturation divisions of the egg may be made 
approximately equal by pressure or by centrifugal force so that the 
difference in size between the polar body and the egg largely disappears. 
Thus if the eggs of the gastropod Crepidula plana are subjected to a 
centrifugal force of about 600 times gravity during the first or second 
maturation divisions some of the eggs in which the axis of centrifuging 
coincides with the axis of the division figure, or spindle, divide into ap- 
proximately equal halves. In my experiments on the eggs of Crepidula 
the giant polar body is usually the second one since the eggs were centri- 
fuged in most cases during the second maturation division; when the 
centrifuging occurred during the first maturation the first polar body 
is the giant one; when it occurred during both maturation divisions 
both polar bodies are abnormally large. Nevertheless only one of these 
cells develops. 
In this animal the spermatozoon always enters the egg during the first 
maturation division and usually at the pole opposite that at which 
the polar bodies normally lie. In normal cases therefore the sperma- 
tozoon is always found in the 'egg' or larger daughter cell and never 
