 Normal diatom reproduction is dominated by asexual or vegetative cell division. In this type of reproduction, an individual diatom will divide and the new diatom cells will reside in two new diatom shells. One which has one valve from the parent and one which has the other valve from the parent. Because this is the way that the cell divides and the shells form, over time the shells become smaller and smaller and smaller. And as a result, if this process continued unabated, diatoms would become miniscule. When the cell reaches a certain size, it becomes fertile and it reproduces sexually, releasing eggs and sperm and fusing into a new diatom cell that forms a stage called an oxysphore. The oxysphore stage is naked in that it does not contain a silica shell. And this oxysphore stage expands and forms an initial cell which is much larger than the fertile cell size. In this way, the vegetative cycle begins again with the size of the diatom restored to its original level.