No. 420.] HISTORY OF STICHOSTEMMA. 999 
process is the breaking of the body wall at a definite point, 
T.e., the appearance of the pore. Immediately after this the 
egg begins to flow out. The diameter of the pore is very 
small, so that the egg is greatly distorted during its passage. 
Indeed, it appears to flow out like rather thick fluid. At first 
a small, rounded, transparent protuberance appears at the outer 
opening of the pore; this is the egg membrane. Then the 
yolk granules and cytoplasm may be seen flowing out through 
the pore, and the part outside increases continually in size as 
more and more of the egg substance reaches it. The part of 
the egg outside the pore and that still within the body are 
connected by the slender band of egg substance which is pass- 
ing through the body wall. The nucleus usually remains in 
the body until at least half of the volume of the egg has flowed 
out. The small size of the genital pore presents an obstacle 
to the passage of the nucleus, and often the passage of the egg 
ceases until some contraction of the body forces the nucleus 
through the narrow duct and it suddenly pops out through the 
pore. After the passage of the nucleus the remaining portion 
of the egg flows out rapidly, and the whole egg assumes almost 
immediately its spherical or nearly spherical form. The sper- 
matozoa on the egg membrane can often be seen clearly during 
the passage of the egg, and it is evident that their movements 
begin as soon as they reach the water. 
It is difficult to understand how definite areas of differen- 
tiated protoplasm could persist or maintain their proper posi- 
tion during this outflowing of the egg. To all appearances, at 
least, the egg flows out like a thick liquid under some pressure, 
and it appears scarcely possible that its parts maintain the 
same relative position before and after its emergence. The 
whole egg is enclosed, however, in a very thin layer of trans- 
parent protoplasm, an ectoplasm, and if the pressure is too great 
this layer is ruptured, and the cytoplasm and yolk flow out asa 
viscid, granular fluid, which tends to reassume the spherical 
form. It is evident that the cytoplasm is elastic and that the 
reassumption of the spherical form by the egg is due to this 
elasticity, Eggs in which the ectoplasmic layer has been rup- 
tured do not develop, or at least development is confined to 
