B. Embrionic Development:
There are three ways an shark embryo can develop: oviparous, ovoviviparous and viviparous.
In oviparous sharks the glands in the oviduct secretes a shell around the egg as it passes through. The mother then lays the egg cases in the sea.
In ovoviviparous sharks the shell is often justa thin membrane with one or more eggs in a egg case. The lining of the uterus in the egg case probaly serves as nutrients while the shark develops. They may even absorb other eggs and embryos for nutrients. In these sharks usually only one embryo survives in a uterus. The female shark have two uteri.
In viviparous sharks the embryo develops inside the mother with all the nutrients coming from the mother through either direct contact between the mother and the pup or through “uterine milk” which bathes the embryo.