Mazon 22, 1912] 
somes unite, or subsequently, followed by a new 
longitudinal split in a new plane, as suggested by 
Janssens in his theory of the chiasmatype. The 
conception of the ‘‘reduction-division’’ is however 
valid, since this division reduces the valence of the 
bivalent to one half, and it fails to take place in 
the case of univalent chromosomes, as is proved by 
the history of the sex-chromosomes, m-chromosomes 
and supernumerary chromosomes in the Hemiptera. 
The explanation of the Mendelian disjunction may 
be sought in either maturation-division or in both, 
as has been shown by Janssens. 
The Penetration of the Spermatozoon and the 
Origin of the Sperm Aster in the Egg of Nereis: 
FRANK R. LInuig, University of Chicago. 
(1) As deseribed in a previous paper, the egg 
of Nereis secretes a large quantity of jelly, de- 
rived from spherules of a cortical layer, immedi- 
ately after contact of the spermatozoon. The per- 
foratorium of the .spermatozoon penetrates the 
vitelline membrane and becomes inserted in a well- 
marked entrance cone. Fixation granules, un- 
doubtedly derived from the spermatozoon, appear 
at the tip of the perforatorium in the cone. The 
substance of the cone becomes differentiated by 
staining reaction and behavior to form an organ 
definitely concerned in the subsequent penetration 
of the spermatozoon. (2) The spermatozoon re- 
mains external to the egg embedded in the jelly 
for 45 to 50 minutes after attachment. The head 
is then drawn by the cone through the vitelline 
membrane into the egg in the form of a thick 
strand of chromatin several times the length of the 
original head of the spermatozoon. The middle 
piece and tail remain external, and may be seen on 
the vitelline membrane up to the time of cleavage. 
They never enter. (3) The chromatic thread rep- 
resenting the head of the spermatozoon then con- 
tracts to form a vesicular nucleus, still attached by 
the perforatorium to the cone. Nucleus and cone 
then rotate through 180° and the sperm aster 
arises always at the point of the nucleus farthest 
from the cone, thus in the position of the base of 
the sperm head. The problem of the origin of the 
sperm centrosome in the egg is considered in the 
next abstract. (4) The ‘‘fixation granules’’ are 
possibly cytoplasmic elements introduced by the 
spermatozoon, though they come from the apex of 
the spermatozoon. No other demonstrable cyto- 
plasmie elements are introduced by the sperma- 
tozoon, (5) After origin of the aster the sperm 
nucleus separates from the cone, and the latter 
+ Jour. Morph., 22, 1911. 
SCIENCE 
471 
gradually disintegrates in the cytoplasm. The 
sperm amphiaster becomes the cleavage amphiaster. 
On the Fertilizing Power of Portions of the 
Spermatozoon: FRANK R. LILLIE. 
If unsegmented eggs of Nereis be centrifuged 
about 60 revolutions of the hematocrit of the 
Bausch and Lomb hand centrifuge in about 40 
seconds, thirty to forty minutes after insem- 
ination, the mass of eggs accumulates at the 
distal end of the tubes and becomes pressed to- 
gether. The jelly, which is of less specific gravity 
than the eggs, then separates from the latter and 
forms a layer above the eggs. In squeezing 
through the narrow interstices between the closely 
packed eggs it rubs over the surface of each egg, 
and in many cases it carries the attached sperma- 
tozoon away with it. In other cases, especially if 
the eggs are centrifuged shortly before the time 
of penetration of the spermatozoon, it draws out 
the substance of the head of the spermatozoon, 
which is very ductile at this time, into a strand; 
and in numerous cases it carries away the tail and 
middle piece, or variable portions of the head in 
addition. Partial sperm-heads of all sizes are 
therefore left attached to the egg by the perfora- 
torium. Such partial sperm-heads then penetrate, 
being drawn in by the entrance cone as in the case 
of normal fertilization, and they form partial 
sperm-nuclei attached to the entrance cone within 
the egg. Rotation then takes place and an aster 
invariably arises in connection with the partial 
sperm-nucleus at the point most distant from the 
cone, %. e., at the most basal point of the sperm- 
nucleus. By using large quantities of eggs and by 
preserving at various stages one can study all 
stages of these processes in sections, and the above 
statements are based upon large numbers of ob- 
servations. It is therefore proved (1) that the 
sperm centrosome is inessential for formation of 
the sperm aster within the egg; (2) the origin of 
the sperm aster is a nucleo-cytoplasmic reaction; 
(3) the sperm-nucleus is polarized with reference 
to this reaction inasmuch as the sperm aster arises 
always at the most basal point of the partial 
sperm-nucleus, with reference to the orientation of 
the nucleus in the sperm head. The conclusion 
therefore involves the conception of a certain dif- 
ferentiation between egg-nucleus and sperm-nu- 
cleus, for the former has no independent capacity 
of initiating karyokinetic phenomena, whereas the 
latter has. 
The two preceding papers will be published in 
full in the Journal of Experimental Zoology. 
