If you're making the New England Lobster Rolls or Chile-Butter Lobster Bao, don't throw away your lobster shells. The body (also called the carapace) and the rest of the shells are a great source of flavor and make a delicious stock. Before you start, though, it's important to know which parts to use and which to discard.
In the photo above, you see a split sack about an inch behind the eyes. It's full of debris and should be from both sides of the body.
The tomalley, or light green matter, acts as the lobster's liver and pancreas. Delicious and prized by many, it lends depth to the stock, but if you prefer to leave it out, just slide your finger under it to remove it.
In a female lobster, you will usually find eggs, or roe, which are dark greenish black when raw and bright red and firm when fully cooked. They're edible either way and give more flavor to the stock, so leave them in.
You can freeze the lobster shells until you're ready to make the stock.