Figure 3.2a, b Fig 3.2a shows a typical fertilised egg 1 hour and 15 minutes after spawning. The egg is at the 1^st cleavage stage and is composed of 2 cells all of which are clearly visible and symmetrical. Most of the eggs 1 hour and 15 minutes after spawning will be at this stage of development. Fig 3.2b shows a fertilised egg at the 2^nd cleavage stage and composed of 4 cells. It is more difficult to see each individual cell but the pattern appears clearly symmetrical. Within a sample of eggs at this time some may be anywhere between these stages so an uneven number of cells is possible. The most important feature is that cell division is symmetrical and remains so past the first cleavage.