Sentence:  The uneven number discovered in the four species mentioned may have arisen in one of two ways : through <WSD>bastardization</WSD>, or through a mitotic abnormality, each of which possibilities may now be considered. In the case of <WSD>bastardization</WSD> of a germ cell with one chromosomal number by a germ cell from another species with a different number, the uneven number eleven might be secured if a paternal germ cell of a species A, with the normal chromosomal number twelve, fertilizes a maternal germ cell of a species B with the normal number ten. 
Meaning of the word marked with <WSD> tags:  The creation of offspring from two different species; cross-breeding.