48G 
L. DONCASTEK AND GHAY. 
first clivisioiE or stages of conjugation. A considerable pro- 
pca-tiou of the eggs is also usually not fertilised. 
The Hybrids between Esculentus and Acutes. 
(i) Esculentus ? x acutus . 
In the eggs of this cross the behaviour of the nuclei appeai-s 
to be perfectly normal. The conjugation of the pronuclei 
differs from that iu acutus ? x esculentus ^ described 
below iu the fact that the sperm-nucleus often reaches a size 
nearly equal to that of the egg-nucleus before the two begin 
to unite, and that chromosomes are visible in both nuclei 
before conjugation. The mitotic figures are like those of the 
parent species, quite regular iu every respect as far as the 
second segmentation division, and no trace could be found of 
chromosome elimination. I'he chromosome number iu the 
first and second divisions appears to be 38 as in the parent 
species ; elimination, if it occurs at all, does not take place 
until a later stage (PI. 28, figs. 4, 5). 
(ii) Acutus ? X esculentus c^. 
4'he mitotic figures in eggs from this cross differ con- 
spicuously from those of the converse cross or the parent 
species, and it is to them that the greater part of our atten- 
tion has been devoted. The conjugation of the nuclei appears 
to take place without serious abnormality. We have many 
examples of the two nuclei lying iu contact, the sperm- 
nucleus distinguished by its smaller size and conspicuous 
central mass of chromatin. Eather later stages show that 
the sperm-nucleus becomes absorbed into the egg-nucleus 
before this chromatin mass breaks up, while the male nucleus 
is still quite small, and before the chromosomes of the egg- 
nucleus are formed ; the rather elongate zygote nuclei with 
an aster at each end, such as are common iu pure acutus 
eggs and in the cross, esculentus ? x acutus cJ, are not 
