18 Transactions of the Royal Microscopical Society. 
life, the multiplication of nuclei seems to be solely effected by 
the process of fission, or direct division. Having observed in the 
chorion of the small normal embryo, above discussed, a number of 
nuclei in the act of multiplying only by this mode and no other, I 
suppose that in the human embryo this process of multiplication 
of cells and nuclei, beginning with the cleavage of the yolk of 
the egg, prevails only throughout the first weeks of embryonic life, 
after which it is superseded by that of gemmation or budding. 
I base this supposition upon the fact that, with the exception of 
the cells of cartilage, I have throughout all succeeding periods 
of development of the human embryo, never been able again to 
discover a cell or nucleus dividing by simple fission. In that 
abnormal specimen of human ovum, probably one or two weeks 
older than the other, I observed, as already stated, the multipli- 
cation of nuclei in the chorion as well as in the embryo stunted in 
its growth, only taking place by budding or gemmation, and the 
same process I observed in the tissues of other embryos up to the 
age of 6^ months. During a certain period, however, the multi- 
plication of nuclei seems to be effected also by the endogenous mode. 
In various tissues of human embryos, of about from 16 to 20 mm. in 
length, as, for instance, the brain, spinal marrow, skin, &c., I met 
with a number of double-contoured cells, which were filled by small 
nuclei of a greenish lustre. On some of them the double contour 
had disappeared, showing the obliteration of the cell-wall for the 
purpose of liberating the nuclei. Another kind of clear cells, con- 
taining a coarse granular nucleus, which in many instances is seen 
dividing into a number of fragments, is met with in various tissues 
of the embryo ; these cells stand very probably also in some rela- 
tion with the multiplication of nuclei. 
