FIGURE 4.2 Life is sexually transmitted (a) Sperm cells surround an egg. (b) As one sperm penetrates the egg’s jellylike outer coating, a series of chemical events begins that will cause sperm and egg to fuse into a single cell. If all goes well, that cell will subdivide again and again to emerge 9 months later as a 100- n-
Meckes/Ottawa/Eye of Science/Science Source