McAllister—Cytology and Embryology. oOl 
received striking confirmation in the work of Moenkhaus (56) 
on hybrids of Fundulus heteroclitus and Menida notata. He 
found that the paternal and the maternal chromosomes have 
very distinctive forms and sizes and thus can he traced in the 
fertilization and the early cleavage stages. They were seen 
to form, distinct groups through the first and second cleavage 
divisions of the fertilized egg, thus retaining their number,, 
form and relative position, for a time at least. 
The cases in which the chromosomes of the male and female 
nuclei are fully prepared for division at the timje of the ap¬ 
proximation of the pronuclei in the egg form the most frequent 
type of fertilization in animals. This is the case in Ascaris r 
Cyclops, Nereis and a large number of other forms. 
For plants the fusion of the sexual nuclei has been commonly 
reported as taking place in the resting condition,—the resulting 
fusion nucleus also remaining for a time in the resting condi¬ 
tion. Prominent exceptions to this general contention are re¬ 
ported for the Grymnosperms. Here Blackman’s observations 
(8) of two distinct groups of chromosomes in the fusing nuclei 
in the fertilized egg of Pinus have been confirmed by Chamber- 
lain (15) and especially by Miss Ferguson (26) who found 
two groups of chromosomes in the spindle of the first division 
of the fertilized egg. Wbycicki (109) found similar condi¬ 
tions in Larix and Murrill (70) in Tsuga, while mjore recently 
Nichols (71) has described two chromosome groups in the fer¬ 
tilized egg of Juniperus. Miss Pace (75) reported that in 
Cypripedium the sexual nuclei had fully formed spirems be¬ 
fore they came in contact in the egg. This, as far as I am 
aware, is the only reported case among the Angiosperms of the 
fusion of the parental nuclei in any other than the reticulate 
condition. I 
We may summarize these evidences as to th© individuality of 
the chromosome as follows: (1) evidences,—of the constancy 
of the number of chromosomes , (2) of the numerical equality 
of the paternal and maternal chromosomes in diploid nuclei, 
(8) of the reappearance of the same number of chromosomes in 
the prophases and in the same position as they disappeared in 
