242 W. WALDEYER. 
be confirmed in every essential. I therefore give the following 
abstracts from Platner’s work (160) so far as he deals with the 
process in question :— 
In Arion the long thread-like spermatozoon does not enter 
at any definite point. The egg-nucleus (female pronucleus) 
remains at the place whence the directive corpuscles were 
extruded (Richtungspol). While the spermatozoon approaches 
the egg-nucleus a clear halo appears round the chromatic sub- 
stance of the head; the latter, as well as the tail, becomes 
colourable, but the tail only so far as it lies inside the egg, 
not that end which projects outwards. 
Several spermatozoa never enter at once ; if a second reaches 
the egg after one has already taken possession of it, it atrophies 
without undergoing any peculiar changes. 
In case the spermatozoon enters before the directive cor- 
puscles are extruded, a larger sperm-nucleus is formed ; 
in other cases this is smaller. As this observation con- 
firms O. Hertwig’s, Platner agrees with him in its signi- 
ficance, that in the first case the developing male nucleus can 
take up part of the nucleoplasm which, during the formation 
of the directive corpuscles, is disseminated in the egg-proto- 
plasm. The remnant of the germinal vesicle (egg-nucleus, 
female pronucleus) undergoes the following changes :—There 
appear in it a number of nucleolar-like bodies of an irregular 
angular form, which at first stain equally throughout. Later 
on they become spherical, and then in each sphere three 
regions can be recognised, a central pale region, which takes 
no stain, and two deeply staining chromatin spherules attached 
to its poles. Each such pale spherule, with its two chromatin 
spherules, Platner calls a ‘‘ karyosoma.” ‘Two stars are now 
formed about the egg-nucleus and the membrane disappears. 
About this time the unaltered sperm-head, around which also an 
aster is apparent, enters the membraneless egg-nucleus and 
loses its aster. Platner would now call the nuclear structure 
present in the egg, in which both male and female elements 
are present, the “ Furchungskern” (segmentation-nucleus). 
The clear portion of the (female) karyosoma now becomes 
