Bony fish and cartilaginous fish (i.e., sharks, skates, and rays) have different reproductive strategies. Bony fish tend to scatter large numbers of eggs into the ocean - take the Atlantic cod for example. These fish lay 3-9 million eggs along the ocean bottom. However, only a few survive. In contrast, cartilaginous fish produce relatively few young. Reproductively speaking, there are two main groups of sharks - those that lay eggs, and those that don't.
The reproductive strategy of laying eggs is called oviparous, and is used by about 40% of sharks. These sharks include bamboo sharks, carpet sharks, horn (bullhead) sharks, swell sharks, and many catsharks.
The eggs are laid in a protective capsule (check out the fantastic image, where you can actually see the baby shark within the capsule). The capsule, or egg case, has tendrils to attach it to corals, seaweed or the ocean bottom. Some inventive sharks (e.g., the horn shark) place their eggs within rock crevices or under rocks to further protect them. The eggs may take several months to hatch, but when they do, the young hatch looking like miniature sharks (so there is no larva stage like in some bony fish).
What about the sharks that don't lay eggs? Those give birth to live young - learn more about them in a future post!