56 MAROUS M. HARTOG. 
meres in the vegetative cells is 24;' that of the progametal and 
gametal nuclei, 12; and the “ basal nucleus” produced at the 
first division of the nucleus of the embryo-sac reverts to 16 
for itself and its offspring, so that of the two gametonuclei 
that conjugate to form the endosperm nucleus the lower has 
the normal, the upper the reduced, number of chromatomeres. 
In the liverwort Riella Clausonii, O. Kruch has found the 
number 8 constant for the inner cell of the antheridium and 
its brood-cells, and the oosphere; the first two cells of the 
embryo have each 16 chromatomeres; but whether the latter 
number is characteristic of the tissue-cells, and the number 
found in the spores, has not been made out. 
In Metazoa the reduction appears usually to take place in 
the gametogonium, and is much more uniform in most animals 
than is demonstrated for plants,” the number of chromatomeres 
being here usually one half the normal; consequently in 
karyogamy or fertilisation as spermato- and oo-nucleus each 
brings an equal number of chromatomeres, the zygote nucleus 
and its offspring reverting to the number characterising the 
species.» This, however, is not always the case; for in Arion 
empiricorum (the Cellar Slug) there are numerous chro- 
matomeres in the oo-nucleus, but two only in the spermato- 
nucleus.* 
The schema of mitosis is sometimes modified in the animal 
gametogonium, the longitudinal splitting of the chromatomeres 
taking place earlier than usual, and even being doubled, so as 
to produce four times the (reduced) number of chromatomeres. 
In this case, which occurs notably in both the male and female 
gametogonia of Ascaris megalocephala, the longitudinal 
splitting does not, of course, occur again in the successive 
gametogenic mitoses; but the chromatomeres, thus formed in 
1 Not 16 as given in his previous paper. 
2 Tn ‘ Malpighia,’ vol. iv (1891). Professor Strasbiirger kindly directed my 
attention to this paper. 
3 It must be remembered that the numbers have only been counted in very 
few cases—at the outside twenty or thirty. 
4 See Platner, “ Ueb. J. Befr. bei Arion empiricorum,” in ‘Arch. f, 
mikr. Anat.,’ vol. xxvii. 
