474 
J. CKAY. 
fertilised by tlie sperm of E. acutus, and so attains tlie 
permeability peculiar to fertilised eggs of E. acutus, no 
abnormality occurs. 
On the other hand, when the egg of E. acutus is fer- 
tilised by sperm of E . esculent us, the E. acutus element 
becomes pathological, as it cannot endure a permeability in 
its surroiinding protoplasm equal to that characteristic of an 
egg of E . e s c u 1 e n t u s . 
Such a change in permeability might well give rise to 
changed osmotic relations between the nucleus or chromo- 
somes and cytoplasm, such as has been suggested (Doncaster 
and Gray [2 a]), as the direct cause of vesicle formation in 
hybrid eggs. 
Th is by poth esis implies that in the hybrids it is 
essentially the female chromatin which gives rise 
to the vesicles. It is impossible to determine this from a 
study of the hybrid eggs, but the effects of hypertonic solu- 
tions upon the eggs of the two species give strong support for 
such an assumption. 
This sug-gestion is, however, in entire opposition to most 
of the conclusions of other workers on hybridisation. Tlie 
work of Kupelwieser, Baltzer and Tennent all tends to show 
that it is the male chromatin which becomes abnormal in such 
cases. Tennent, however, has shown that in the crosses 
Arbacia x 'roxopneustes not only are all the chromo- 
somes which are derived from the male eliminated, but also 
some of those from the female parent. Again, G. Hertwig 
has shown that fusion with an abnormal sperm can cause the 
female chromatin to be affected. 
Again, abnormalities are to be entirely confined to the male 
element in the egg, there is apparently no explanation for 
the cytology of such reciprocal crosses as SphEerechiuus 
X S t r 0 n g y 1 0 c e n t r 0 1 u s , or E c h i n us a c u t u s x E . e s c u - 
lentus ; for if, as Baltzer suggests, the male chromatin goes 
wrona" because it is “ out of tune ” with the female cytoplasm, 
why are not both reciprocal crosses abnormal ? And in the 
case of E. acutus c? x E. esculentus ? we should expect 
